I've been using a Mooncup (uk) for about 4 months, and it tends to leak for the first two days or so, and after that it works without any problems. The first two days of my period, the cup rides a lot lower (I think my cervix is much lower then) and the cup leaks a lot, especially if I'm doing active things like hiking (terrible time to have a leaky cup!). Sometimes I'll take it out and find that it's not even half full, but still leaking. I have to wear a pad as a backup, which I really had hoped to avoid doing.
Then, it works fantastically from about the third day onwards when there isn't as much flow. The cup tends to drift way up and can take a bit of coaxing to remove it, but it's nothing unmanageable.
I don't think the leaking is because I've positioned it wrong, because I use the same fold the whole time (7 fold) and that works from the third day onwards. Its just the first two days when I have a heavier flow that I can't get it to stop leaking. Any advice??