I owned a 2012 X5 diesel then a 2018 Audi SQ5 (similar to the X3 M40i, not the X3M) and switched to the MY this past September. Now that I have ~4,500 miles on it, I am extremely happy I made the switch. I don’t think you’ll regret it at all.
The MY has 5 cubic feet of more storage space (with back seats folded down), 68 vs 63 (SQ5). However, the rear hatch is sloped on the Y so there is a little less vertical space. I do motorcycle track days and one concern I had was if the Y had enough storage space to lug all my track gear and I’m happy to say it has more than enough.
As for other posters’ comments about service quality from BMW, etc., I have to say, my experiences from owning MB, BMW, and Audi were average. Nothing was exemplary, all was just a standard service transaction...well, except for the BMW where the car wash guy kept stealing all of my quarters out of the car (I leave about $3-5 in the car for parking meters). Had to bring it up with the service manager 2x and both times he just gave me a roll of $10 in quarters.