After handling a P-365 in the store I felt like the grip was a hair too short, and was glad they made an extended 12 round mag, but after shooting it discovered I shot the 10 round mag just as well. I carry it with the 10 round mag, and I don't even always have the 12 rounder with me, but when I do, it's the backup.
Thin but not too thin.
This is it for me as well. I had a 9MM Shield and liked it, but the very slim for the front to back width made it want to turn/twist in my hand when pulling the trigger/firing it. I really had to concentrate to stop this. I shot it well, but with more mental effort than the P-365. The P-365 is a breeze to shoot well. Front sight squeeze. That's it.
I'll be shocked if I change my mind and do not buy a P-365 XL, with the red dot of course. No need for it (For me) without the red dot.
Oh, and I hope the Romeo Zero has a large dot, as they are so much faster.