I'm assuming you're talking about having an actual Explorer or Landranger map appear on a GPS screen rather than just the routes you've planned in the software.
In that case (and trying to look at this objectively) as far as I know, the Road Angel is the only one you can load the actual maps from Memory Map onto.
Other GPS units, such as Garmin, use their own proprietry mapping software like TOPO.
The Road Angel comes with all the National Parks (at 1:50,000) pre-loaded plus you can load your own Memory Map Landranger or Explorer maps onto it.
It can still be used as a standard "on-the-road" GPS with voice directions and safety camera alerts.
Memory-Map also say it is waterproof and rugged for outdoor use but just how rugged I wouldn't like to say.
I do like the new Satmap Active 10 which has been designed from scratch for outdoor use, but it's £300 PLUS you still have to buy the mapping for it at nearly £100 a go.
I think if you have quite a few Memory Map CD's, the Adventurer will not only be the best one to put them to use but probably the only one that will accept the maps on-screen.
If any one knows any different, hopefully they'll let us know.
David