On the London to Whitstable ride, I made use of my Samsung S5. This let me make use of the apps on my phone, rather than my old Garmin unit for showing directions.
I sold my Garmin recently - this was partly down to the fact that I could use the Samsung for navigating and partly because I never seem to have the Garmin with me, but my phone goes everywhere. The Samsung is waterproof (and I've tested it - though, I'm not sure if it's water resistant or water proof - there is a big difference!). However, there were a number of issues of using a phone as a navigation device.
The first issue I had to resolve was how to attach the Samsung to the Brompton. Obviously the Garmin came with the required kit to attach it to the bike as that's where it was supposed to go. But the Samsung required some third party equipment to attach it. I spent some time looking around for a device and I came to the conclusion that either the Quadlock or what I went for in the end, the Tigra case for the Samsung would do what I wanted. There was little difference between the two but I went for the Tigra on the basis that I could see that I could charge the phone whilst it was mounted (I only assumed you could do it with the Quadlock) and that the mounting system looked more stable. The Quadlock seemed to be the same as Garmin - using elastic bands to secure the mount to the handlebars, whilst the Tigra used a tightened strap. It should be noted that whilst the Tigra can be fitted and removed from different bikes, it is harder to do so than on the Quadlock, so if you've different bikes you want to be using the phone on, you might want to investigate the Quadlock in a bit more detail.
Mounting to the Brompton was easily done and doesn't really affect the fold on an S type. There's some degree of touching but this hasn't caused an issue yet.
With the phone mounted, the other two issues to address were navigation and battery life. Using the screen of the phone and the GPS will cause the battery to deplete pretty rapidly. On the London-Whitstable ride, the first two hours were on battery alone and the battery dropped by 50 percent - clearly not enough to get to the end of a 11 hour day (as the Whitstable trip was). So I'd purchased a battery pack on Amazon to plug into my phone. This would live in my Mini O bag that tends to go everywhere (at least in longer rides) with me and I'd run the cable to the handlebars. That was easily solved. Since writing this, Amazon have recalled the battery pack I've linked to above as there was a risk that is was damaged. Using damaged Li-Ion batteries is not recommended!
The navigation issue could prove to be an issue - Google Maps offers turn by turn navigation but doesn't have a full set of cycling routes built into it so it makes it harder to navigate. I looked at Strava and Ride With GPS as the navigation apps - Strava because I was already using it for day to day tracking and Ride with GPS because I used it for programming my routes, so it would seem the best option for riding the routes as well.
The Strava website features a route builder for creating and riding of cycling routes, but it does note that this is only in Beta at the minute, so I guess a number of teething issues are to be expected. However, it performs reasonably well for an item that is in Beta and the limitations are probably due to the mapping software they use (Google Maps), rather than the Strava website itself.
Creating a route in Strava is a bit of a pain - no importing from elsewhere so you can't copy anyone else's route and import it to follow without planning it yourself. However, you can (if you have a premium subscription, add other peoples rides on Strava as a route). I tried recreating Mark's Whitstable route on Strava and was left plotting the route manually. However, issues arose where there were one way streets with counterflow bike paths and with cycle paths themselves (such as an area where we crossed the Medway on a cycle/footpath). These weren't on the Strava/Google Maps route planner and the software would try to do a detour to get to where we wanted to go, clearly not ideal.
I tried it on a different route to see how the directions would work - how to get to cadets, something I know well as it is through Welwyn itself. Strava was a bit disappointing in that regard. The map was purely a "breadcrumb" trail - no directions or warnings, just a route shown on the map and you take responsibility for keeping yourself following the track. Rudimentary I guess but it does work. This is what happens on the Garmin when you put in a GPX file to follow, rather than a TCX file (in my experience anyhow). This means you've got to keep an eye on the track often, in comparison to if it was turn by turn with warnings. It also means that you have to keep the phone display on constantly to view the route.
Overall then, it's not ideal, though it's big plus is that it's free. It would be nice to see some turn by turn directions and import but at the minute, it provides a basic route finding functionality. I know the routes for the RAFBF Challenge Ride are on Strava and Strava are mapping partners. However, I might be looking at other alternatives - though if it's all on roads, I might be ok.
Ride With GPS
Ride With GPS offers the ability to plan your cycling routes online and then download them to your phone or GPS device to follow. It also offers cue sheets so you can print and have a copy as a paper copy in case your batteries die on your navigation device.
When planning your route, you can use a mixture of Google Maps. Open Street Maps and Ride With GPS's own maps. This means that you can probably get exactly the route that you want or need as the Open Street Maps and RwGPS maps are actually very good with cycle paths and footpaths, something that Google seems to be missing in places.
In addition to the route planning, RwGPS let you follow directions to get to where you need to go. This route finding is only open to those with a premium RwGPS membership, which is available for a small fee monthly or yearly. This gives some benefit over and above using a Garmin as the maps are updated automatically for you and you can use one website/app to track rides and to direct you. However, I can understand some peoples reluctance to pay for a service when with the Garmin, you can pay for the device and then don't have to pay anything for additional maps (if you use the freely available maps - Garmin and Ordnance Survey maps require ongoing payments for updates).
The RwGPS app took some setting up and getting used to. To start, it can override the Android devices functionality of turning the screen off. However, this seemed to need some playing about to sort out, as it could be set to be always on, only when the device is navigating or following a route and it could be set so that it only lit up when the directions appeared on screen. Likewise, you can adjust whether the track follows the directions (so your direction of travel on the screen is always up). When riding, I find that occasionally I didn't hear the warnings for the turns so I ended up missing them, however, I adjusted this for the Mosquito Practice Ride that I did and I ended up hearing the warnings then - the warnings are displayed on the screen.
The warnings and turn by turn directions are ok, but they can (especially in the case of warnings of off course), take up the whole screen and make life difficult to correct your course without pressing the dismiss button.
A feature of RwGPS that attracted me to it was that it can download the routes you ride and store them offline - this includes the maps. This means that you can go out cycling and be happy that if you don't have a mobile data signal, you can still find your way around. However, this seemed a bit awkward until I figured things out - on the Whitstable ride, I left data on and I managed to lose signal along the way - the maps disappeared but the route remained as a red line on a grey background. Not the most useful tool then, but would allow me to follow the route. I find when doing a later ride, that the trick is to switch off data. This then forces the app to use the download map tiles and I didn't have any issues then at all.
For me, RwGPS is a much better tool for navigating with. The route finding was better online and the maps are much better for following, though it comes at a cost. However, Strava does display information better for just wanting to know your riding stats, such as time, distance and speed as it has a single page for this, whereas RwGPS displays the data along with a map.
Using a phone as a navigating tool on one hand beats using a Garmin - the screen sizes of the smart phones I have (iPhone 6 Plus and Samsung S5) are significantly bigger than the Garmin and so allow a much greater ability to see where I'm going. However, they're let down by the water "proofness" of the phones themselves and the battery life. Without a battery pack, using a phone to navigate might see you run out of juice before the end of the ride. I found that using the battery pack above, I was able to charge my phone whilst I was riding and it would end up slowly charging the phone as well (so it was supplying more power than the phone was using whilst cycling).
Whilst you might have a smart phone, a mapping Garmin is likely to cost you £200-£300. At that rate, you can use RwGPS paid for version for about 6-7 years (£30 a year for RwGPS) before you'll equal the cost of the Garmin. You also have the ability to upload and download data to the phone on the fly if you need to or to upload your Strava rides!
Accuracy seems reasonable to me - it allows me to navigate successfully and that's the big question. I have noticed that Strava uploads that peak speeds seem perhaps a bit far out and that occasionally the tracks in Strava seem a bit less accurate using my phone than perhaps if I'd used a Garmin. I don't think that'll put me off to much though.
I think for now I'll continue with the phone - after all, I always have my phone with me, but I rarely carried the GPS.