I use Ram mounts for both GPS and radar detector. The Nuvi line is much cheaper than the Zumo. But, if you want to spend the money, I'm sure you'll like the Zumo.
I went with this one and it worked out great (have a Navigon I put inside). Not chrome, but that's my only issue with it. No bouncing, held up well in the weather, etc. easy on/off if you don't want it all the time. Arkon GPS032 Handlebar Mount for 3.5 - 4.3-Inch GPS Devices
You pay a lot more for that waterproof-ness. Behind a windshield, using a zip lock bag when really necessary, I've never had a problem. It takes a couple of seconds to pop it out if you have to, but a little rain won't hurt them at all. If you regularly ride in heavy rain I'd probably consider the Zumo, if not I'd save the money.