I have used Horsham Car centre MG for aftersales and they have been great. Not so impressed with the sales side, but I ordered my MG before I even knew they were a dealer, not that they were the closest to me, as there was one in Tadworth, which is closer, until they went bust, but again, I didn’t know they existed either until after I had put my deposit down back in July 2019!
I’ve had 2 BMS updates, December 19, the 2nd Generation Comfort System update, the High Voltage Fuse update, the door wiring loom warranty replacement, padded out the A pillar speakers to get rid of the rattles, the BMS update that allows the car to charge while unlocked and the battery heater update (not recommended).
I bought some TPMS sensors from them that they had on the shelf.
I do seem to know more about updates than they do! But they have had no problems with doing them.