The Square
Purchased an end of season 2024 Wilson A2K M23. Finished the initial break in before the end of fall ball and purchased this to hold form over the winter. So far, mitt is holding form extremely well. This is my second form, the first being a 3 Grande for first base. Both bags are slightly small so expect the top of the pocket to stick out. This does not impact the bags performance beyond not fully sealing the mitt from elements.
If you like box-style break-ins just get the Square and be done with it. I have tried several decent options but nothing is quite like the Square. The molded insert fills the pocket space and the exterior neoprene sleeve wraps around the glove and cinches it down to the molded insert keeping the shape identical to the molded insert at all times. When you take the glove out it is shaped better than any other option I have used so far. I initially bought one of them and now I own four.