The Dynavin unit does look good, but requires too much messin' around and jury rigging to make all features of car function as they should
You will lose both the SOS system and any/all of your audible chimes. Also, If you have certain repair issues needed with your car, it is imperative that the factory HU remains installed. One I can think of off hand is if you have a fuel pump problem. It sounds ridiculous, but the factory HU is tied in with rest of control modules in the car and needs to be present for dealer to program/reprogram/update the software.
So basically, if you install the Dynavin, and you want to retain SOS, all your Chimes, and not lose the ability to udate your car software when needed, you will have to either mount your factory HU in the trunk area with a bunch of special wiring/cabling adapters (and extra speaker(s) hooked up to only factory HU for chimes) so it is present in addition to the Dynavin at all times, or at the very least, you would need to re-install the factory HU when the time comes in order to allow the dealer to be able to repair certain issues with your car.
Both of these options suck and are too much trouble IMO...
BMW has successfully made it very difficult to integrate aftermarket electrical items (or even add OEM options in alot of cases that didn't come with your car originally). You are better off buying the car with the options/features you want from the beginning - it's easier and cheaper
As far as Bimmian goes, I have purchased several items from them, never had an occurance that required returns or warranty issues, but they are higher priced than JLeviSW (they carry all the same products as Bimmian).
I do agree that CarAudioCraze has the best pricing on the Dynavin (or at least they did). That is where most of the members purchased from a while back...