The trouble with taking the car to BMW for an MOT is that, IME, they delight in finding other things that need doing! Luckily, as an MOT is a standardised test, it shouldn't matter where you get it done and no-one would ever get away with claiming that the resale value of your car could be affected if it didn't have a history of MOTs carried out by the main agent.
For the past several years I've taken my cars to a small chain that only did MOTs - no exhausts, no brakes, no welding - they let you book timed slots on-line so it's done while-you-wait and, if you book in advance, you can get up to 50% discount - so if you book 90+ days in advance, the MOT is £27.
The only caveat to this is that they've now started doing minor servicing and repairs so I'll have to wait and see if things change, but past experience has been good as the one time they found something - a rear bulb had gone (and I'd checked them before leaving home) - they were happy for me to nip up to Halfords and buy & fit a replacement. Went back down, showed them it was now working and they issued the certificate, no fuss, no bother, just excellent customer service.