I've been using the Nuvi550 for maybe about 6 years now. For the first few years, I was using a 99cent ebay mount. It actually lasted for about 100,000km of use. Then one day, about 3 or 4 years ago, I was riding on Southwood#13 and I look down and can see it shaking a little bit. I might have been riding around 80-100km/hr at that point. I think 'wow my GPS is moving around a lot - that's weird..." I lookup at the road for a bit and next time I look down, my GPS is not there anymore. I'm still moving at a good clip and look in my side mirror and can see it bouncing down the road way behind me.
I turn around and go get it. The outer bezel was totally destroyed and there were all kinds of scratches on it as it lay in the middle of the road. On my way home, I stopped by Radioworld and picked up a RAM mount and have been using it ever since. The Nuvi550 takes such a beating and still works perfectly to this day. I have ridden in constant heavy downpours all day without this thing having the slightest hiccup, and not to mention all the super bumpy gravel roads and so many times i have dropped my bike and this thing goes flying off the bike. I must have put on close to 200,000km on this thing and the battery still lasts close to 8hrs. I bought on closeout for under $200 from NewEnough way back when...
I have read so many stories about different issues with so many GPS brands models... I wish I had tried a Streetpilot 2720 or whatever it was... those seemed like really good units too.