The installation in a BMW is not easy, so if you have a negative self-concept of yourself as an installer, you will start swearing heavily about 1/2 of the way through. I'd leave it for the pros.

Now, as far as who "BMW" uses, BMW doesn't offer this as an option. YOUR BMW DEALER might offer it, using a local "dealer expeditor" as a subcontractor for the work, but it's not officialy BMW sanctioned or anything. It's their local decision if they offer it and who they use, not BMW USA's decision.

The only trouble with dealer expeditors is that they operate with heavy cost pressures, and are used to finding the cheapest parts out there. Even if your BMW dealer doesn't pressure them the way the Chevy dealer does, they are used to being so pressured - and most of them carry pretty low-end products in order to hit a price point that allows the car dealer to mark it up again and make some profit on their end.

So I don't know where you are geographically, but if you are looking for the "best", you can usually find that at the right aftermarket specialty install shop, but not in the dealer sales add-ons. Those probably work OK, but they're not the best.