My GPS mouse (BU330 from ebay - Hong Kong) works awesome, I highly recommend it. I never need to wait for it to lock.
I bought a USB extension cable (6'). Not sure if you may have a problem longer than that.
I don't think it works well under metal. I have mine in hidden on the front dash (where the tweeter goes. It's hard to notice unless you're looking for it. I haven't tried with the plastic cover (I will soon). I heard some people have put it in their glove boxes and lost a few satellites but it works. Some people have problems unless its literally on their roof.