I have one myself and have been pretty pleased with it. It was recommended to me by another forum member. It does take a little getting used to, especially when it comes to mapping etc. But once you are used to it, it's a really good tool, and extremely bullet proof. I recently had a crash and the Garmin survived with use a little crack on the screen. More than can be said for many other things I was carrying!

You can use Open street map on it. I download my maps for free from here, which come garmin ready:

Free worldwide Garmin maps from OpenStreetMap

You simply copy them over to the root of the SD card or internal memory when you need them. I only ever load one map per country, as having too many maps on there seems to slow things down. You can also use custom maps. I have made custom maps by scanning paper maps / photographing / screen capture and georeferencing the images and then uploading them to the Garmin.

As for the screen size, it is very small, but that does not bother me. I do all my planning from a large paper atlas, or a computer with a large monitor. I would just get too frustrated planning the full trip on a tiny screen. Once I plan it that way, I then upload the route to the Garmin using basecamp, or I write down key points along my route and simply plug these into the garmin as I go.

Hope this helps