I use one of these as a backup to my fixed mount Lowrance LCX-25C. A big part of the appeal was that both units accept Navionics charts and that I could pre-load a zillion waypoints on the handheld and then transfer them over to the fixed unit.
The handheld does eat batteries as was pointed out, and you might consider a unit that you can "plug in" to a power supply. The iFinder will do that, so I can plug it in to a cigarette lighter-type outlet, and also use in in my truck...
Both units are waterproof.