I tried these the other night. I myself do not posses anything near high level ring-strength, aside from training primarily gymnastic static holds. However I was able to get 2 of them in singles. I think big limiting factor for many people may be how they execute a majority of pushing exercises. I notice a lot of people in my gym that execute their pushups and handstand pushups with their elbows flaired out to the sides tend to not be as comfortable on the rings, when they are forced to keep their elbows tucked in.
Elbows turned in is something I focus on when training the planche or handstand. So I guess training elbows in can have carry over even at low gymnastic strength levels.