I use one because I seem to be allergic to pads and tampons, so really could do with fixing the leak!
I successfully used it before I had DD. She was born by c section and I didn't really go into labour with her (waters broke but didn't dilate much before going to theatre), so things shouldn't have changed down there. Nevertheless, since my periods returned I have only had about a 50/50 success rate (whereas it was bombproof before!). Sometimes it just leaks a little, but if I go to the toilet in between removing it, sometimes it slides down too.
I really don't want to have to go up to the bigger size because I find removing it uncomfortable as it is. But I don't know what else to try! (Have already checked the little holes aren't blocked by inserting a pin).