i recently bought a mooncup uk to replace my keeper mooncup, which was driving me crazy -- it was always shifting around and slipping too low and being generally uncomfortable. i'm on my fourth day with the mooncup uk, and the difference is *astronomical.*
to be fair: my mooncup uk is the larger rim size, since i'm 30yrs old now. my keeper mooncup, which i bought well over a year ago, is the smaller size.
but the differences between the two can't be because of size only:
the uk mooncup seems about 15% thicker, a good bit more sturdy, which means it pops open far more easily. previously, it would take me several frustrating tries (often accompanied by swearing while stuck squatting on my bathroom floor), to get my keeper mooncup inserted comfortably and open/suctioned properly; the mooncup uk opens the first time, every time..., even when i'm inserting it while sitting. never have i had to do anything more than twist it a half turn to get it open. and once it's open, it automatically positions itself comfortably.
unlike my keeper mooncup, most of the time i don't even feel the mooncup uk. nor does it slip around half and much. and if i do have to reposition it, it stays repositioned for a good length of time.
the mooncup uk has gripping rings at the bottom of the cup,which the keeper mooncup doesn't have -- meaning that the uk mooncup's unquestionably better suction isn't an issue when it comes time for removal.
although i've trimmed the stems on both to the same length, the mooncup uk is less tapered at the bottom, which makes it less pointy (and less 'ouchy') than the keeper mooncup.
also, as i mentioned in another post, the mooncup uk's instruction manual is FAR superior to the single-sheet-of-xeroxed-paper instructions that came with the keeper mooncup.
i hope this is helpful to someone out there when deciding which cup to buy... mooncup uk or bust!