I wanted to love these shields. I have the 24mm and have been using the 21mm inserts or BeauGen cushions in them with good success. I was hoping the 21mm shields would let me ditch the extra pieces and cut down on the things I needed to wash every night. Unfortunately, these did not work out for me. It seemed like they were a little different design than the 24mm and actually caused a bit of friction and pinching. A noticeable difference was that the rim of the shield now has a cutout where the backflow connector and tubing come together. In theory it seems like a good idea, but you have to take extra care to line up your pieces. Pulse, when you go to pour the milk from the cup to another container, milk now flows out and over the opening to the backflow connector. If you’re like me and refrigerate your cups between sessions, you must take great care that no milk leaks into the backflow connector, which could get into your pump and ruin it. Long story short, I’m back to using the 24mm with the 21mm inserts.