There was a review/discussion on WUS about Sinn U1, the OP explained why the bezel is like that. Here is the post:
https://forums.watchuseek.com/showthread.php?t=4402650
Edit: to save everyone the trouble of clicking a link, I would copy the text and quote the OP here.
Original posted on WUS, by
rabbit3001, on June 8th, 2017
"It's true that the bezel on my Black Bay felt like heaven. It was just a pleasure to operate. But boy, once either the watch or my hands (Lord behold, or even both) came in contact with the slightest amount of water, the bezel jammed regularly and I simply couldn't even get a grip on it. That makes it useless for actual diving if you ask me, as a nonprofessional diver.
Now looking at my U1, yes, the bezel has play in every direction and it doesn't feel nearly as satisfying to play with it but it is THE perfect bezel for actual diving.
Just like the lume of Sinn watches, the bezel is just thought out all the way through.
After asking Mr. Schonefeld about the function of the bezel, he again revealed to me what Sinn had to incorporate into their design, in order to create, in my opinion, the perfect dive watch bezel.
First of all the bezel has to be operable at any time, in even the harshest environments and maybe even with the thickest gloves on. That's why Sinn designed the bezels on their diver's watches to be a tad looser so that the diver can operate the bezel using one thumb only. That's also the reason for these pill-shaped cutouts on the edge of the bezel. Apparently they turned out to offer the best grip in even the most severe conditions.
I can also confirm that out of all my watches, the bezel on my U1 is by far the easiest to operate at any given moment. Furthermore, a little bit of room or play under the bezel is needed so that dirt, salt - or even ice crystals won't build up as easily, which might, in the end, lead to an inoperable bezel. Needless to say that no serious diver or operator would ever want that to happen. While enabling all these features listed above, the bezel is still extremely secure and mine has never moved unintentionally.
Simply put: Sinn's bezels are designed for real divers. How often did the bezels on my other watches get stuck after swimming in the ocean? I stopped counting by now. I mean yes, that was always fixable by putting the watch in a sink full of warm water back in the hotel room, but right "in the field'" the bezel was useless often times.
So please keep that in mind when buying a Sinn watch as I've heard even very seasoned watch reviewers complain about the odd bezel action. "Click to expand...