My impressions...well, counting this one, I've had 55 motorcycles. My other ride currently is a '22 R1250GS. I first bought a Yamaha Zuma 125 and it was really fun but a bit small and slow. For a "grocery getter", and quite a bit more, the 400GT is surprisingly good. Build quality is typical BMW and the performance is pretty impressive, especially for a scooter. I do wish it had better suspension though.
The main thing standing in the way of riding a scooter, especially for older, experienced riders like myself, is ego (my opinion, of course). At age 78, I don't much care anymore what others think and I do whatever I like. I know it's not particularly smart but I jump on my scooter with shorts and a t-shirt ( and a short helmet, of course). And, it looks appropriate on a scooter, if one cares about that. I'll tell you this, it sure is nice in hot weather. It would look silly to dress like that for the 1250 GS and it probably wouldn't make a lot of sense due to much higher speeds and more spirited riding. For the big GS, I usually go ATGATT. Anyway, I love the 400GT for short trips and errands and it's just great for jumping on and going for a ride.