It's the best one if you want standard stats (everage speed, etc) and navigation rather than fitness stuff (cadence, power, etc).
You can pre-plan routes with Mapsource, which is really quick and easy. You can also drive a route in your car, save the tracklogs and then repeat that route on your bike. And yes, you can ask it to plot routes on the fly.
It's pretty small and light. You'd normally mount it on your handlebars (there's a handlebar mount available for about £13). As I have a trike, I have it mounted on a Space Bar attached to one of the handlebars.