Have we bought the Sitzverkleinerer after we realized that our small but is a bit too small for the Safe Sleeper. It is like or slipped back and forth in bumps it was not fixed in it. Thanks to the seat reducer it is now perfectly in the bowl. Thinking they will still fit about 1 month in there. When it comes to my child's safety, the few bucks is not too much for me. So I can Sitzverkleinerer all whose baby is very small only recommend.