I have the unit and agree that it does block the left-hand mirror somewhat, but not completely. The intercomm and CB quality is very good, as it should be for the price. I bought it primarily for the high-quality intercomm and have not been disappointed. I've used an MP3 player with it, but you are severely limited by the quality of the speakers in the helmet. There is simply no low-end (bass) response in most speakers as they are designed to give clear voice reproduction. I also prefer to ride with earplugs, so it's tough to listen to music. The CB and Intercomm can be heard through earplugs, but my wife doesn't like wearing plugs so volume selection is a bit of a problem.
The weather function is great, but you won't use it that often. You can tell when it's raining without too much help.