For autorouting, all of them will be next to useless without some serious add ons in the way of mapping.
The base map in the Garmin units will give you the biggest towns and cities with an accuracy of a half ,mile or so, but that's about it....
There are several ways around it though......you can get Touratech QV West Africa, which is based on some fairly out of date Russian Topo maps.....you upload them into the unit as an overlay and if you can work the software, you can create some pretty good routs based on waypoints......to use it effectively though, you'll need a laptop to upload new sections, as there aren't enough WP's available to do a decent route.
You can do the same with some PDA based solutions, and you can use your own maps sometimes.
TBH, the the route is pretty simple anyway....with a couple of maps, a sense of direction and some common sense, with a bit of hand waving and a smattering of French, you'll be fine
The best use of a GPS though is for the Western Sahara crossing.....there is a very good tarmac road right the way through from Nouakchott to Nouadhibou now, but the traditional off-piste route is pretty well mappped out...I've got a set of WP's that Slimbo, Tony and I did a couple of tears ago, and it's well covered in Chris Scott's book as well.
There are also databases out there with many of the petrol stations in WP form.....again though, things change so quickly that they're not too relevant.....in the space of 12 months, the road was built and several Touareg camps set up selling fuel...we also saw three or four petrol stations being built in January......it's a little sad really....I wouldn't be too surprised to see a ferking Little Chef in the middle of the Sahara when I go down next year
