I don't have a Garmin, but I have a handlebar mount for my Mio C320, which has a 4.2" color touch screen. I don't always put it in the handlebar mount (sometimes I keep it in it's case in my panniers), but I always have it with me when I ride. I find it very useful; I've got it running MioPocket, which essentially turns it into a PIM, which also allows me to install other CE-based software. In addition to the MIO navigation software, I've got Ozi Explorer CE, which is great for off road use (I downloaded the USGS topo maps for the national forest that I live in--most of the forest roads aren't on any of the commercial GPS software). When I'm heading somewhere I haven't been before and I want navigation instructions, I use the txt-to-speech functionality of the MIO so I don't need to look down at the screen. If I need to look at the screen to get my bearings, I'll pull over and stop.