Seems unlikely to retain everything you get from the factory head unit. I'd want a better guarantee than the description on the web site -- with a money back option and i'd be prepared to deal with install and uninstall costs if it doesn't work.
The head units from BMW are pretty good. Flat output, can be coded to send analog or digital out, and then you maintain the original look of the car. I've never seen an aftermarket unit that looks "right" in our cars, IMO.
Euro spec wide angle mirrors; Dinan front sway bar; sport wheel + flappy paddles; staggered sport rims with Conti ExtremeContact DW. JL Audio 600/6 + technic harness; Gladen Audio 8" Woofers + musicarnw adapters; Morel Hybrid Ovations. Project pile: 2 sets of rims, more staggered and less; M3 flappy paddles; Msport factory suspension: front & rear sways, springs, & struts.