i had something similar on my old E46. was quite buggy at times but was cheap, had pretty much everything you could ever want (bluetooth, sat nav - mine had iGo which was perfect, wifi, tv, dvd etc etc) and the torque app was pretty cool running it through the OBD2 port. if you go there be prepared for issues though and you will want to be relatively techy. i never had really serious problems but there were plenty that did.
i would just say dont go for a wince based one and stick with android. if i didnt have rnse i would definitely get one