I have used my USB port for power for my eTrex since I got it, works great. I started out running without the batteries, but did not like not having power on removal so I run with batteries and USB power now. I don't think the Kawa vibrates enough to cause battery terminal damage, but I have a vibrationless mount of my own design.
If you put the wrist band on your GPS, then just tie it around your handlebar, so if it comes out of the mount it will start flying around but not be left somewhere out on the trails.

 

I use the Etrex with the handle bar mount. One word of caution. Use a leash and tie it to the bars. This has saved mine twice! If you use the handle bar mount, put a little Locktite Blue on the screw that holds the mounting clip to the GPS. The leash saved mine because the screw vibrated out.

 

Just ordered a Garmin Oregon 450 with BC Back roads maps.
Dang map cost just about as much as the GPS! Hope it's worth it.