Yep. Distance allowed, but not elevation. They can obviously zero in on the pin but the pros are thinking about several other yardages on every shot.Yeah, the PGA of America started allowing them a few years ago. You don’t see them much.
GPS are allowed too but I don't think they're accurate enough for the pros. IIRC the best you're going to get there is +/- 2-3 yards, which is an awful lot of inaccuracy for these guys.
Edit: and yes... it looks miserable playing in this today.