The Keeper uses small holes around the rim that create a suction when it is inserted. It rarely moves. If it does, you just give it a little push back up.
Because there are no strings, you don't get that gross leaky feeling from the string getting all wet when you pee. When you wipe, it wipes up any Keeper mess, too.
I use the Keeper from the beginning of my period - when I just get little bits of the brown junk - to end. No problems at all. I am thinking of trying it during ovulation when I get super gooky. I'll let you know how that goes. Unless, of course, it is too much info for you guys.
BTW, aarealsei, I can't figure out what your avatar is...can you post up a larger pic here? It kinda looks like a monkey, but I can't imagine anyone here having exotics.