chimera said:
....the Garmin GP12 is still the best model around for military and demanding exped use, as it is rugged, and has 4 LR6 batteries (most hand helds only have 2). It is easy to change between the grid systems that you will find on UK and US issue military mapping, and Lat/Lon for foreign maps that are often not gridded.
I've had one of these for a couple of years and found it very useful in a number of places. It eats batteries - a set will last about 12 hours if you leave it switched on.
It is optimised for vehicle nav using waypoints: it has a good track keeping facility and would be ideal for desert or ocean use, or even basic aviation use. It doesn't have a proper map display, unlike some more modern (and more expensive) models. For surface nav in close country, its best use is as a fixing aid, and for finding your way back to a starting point if you become temporarily unsure of your position.
Like all electronic aids to navigation, it should be backed up with more basic techniques, such as map and compass. If you mix the information from two different systems you will probably get something that is better than either alone - but I wouild say that combining GPS with map and compass requires greater skill than using either system by itself.