Before you even consider doing this, you must be confident using an OS map. The terrain is vast (on day two we didn’t see a soul for most of the day) and can turn nasty at any time.
As a group of six we had two sets of maps and three GPS units and a smartphone with the Back Country Navigator software.. If you are relying soley on maps you will take significantly longer to find your way across Wales – it just takes a lot longer, no matter how experienced you are.
Explorer 201 (Knighton), 200 (Landrindod Wells and Elan Valley, 214 (Llanidloes & Newton) and 213 (Aberystwyth & Cwm Rheidol).
We used a Garmin 605, a Garmin 705 and a Garmin 500. Any of these three will get you from Knighton to Aberdovey with absolutely no technical skill required – you literally follow a line on the screen. Apart from this being a fantastically easy way to navigate it also gives useful information en route, such as distance travelled, and distance to go. It also flags up useful information (shop open 8-12 etc).
The smartphone worked well as a backup, and is very good at pinpointing your exact location, but it doesn’t give you a line on the screen to follow.
We used the GPS files from the IMBA website. These files are computer generated, not ‘ridden’ files and so are not quite as accurate. Saying that, we had 100% confidence in the route at all times. If there are only a couple of you I would have at least two units and a map as backup. Both the 605 and the 705 had a ‘funny 5 minutes’ which wouldn’t have been quite as funny if they were the sole means of navigation.