I have had a mooncup for almost a year now. At first my periods were horrendously heavy but I just changed it 2 hourly and found that I was much more comfortable than before when I had to use tampons and pads and still change them 2 hourly With very heavy periods I still used it overnight, but would use a pad as well to stop leakage onto my clothes (or get up in the middle of the night and empty it). This was less of a problem than using tampons and pads and still leaking through every morning.

Now I have a mirena which has stopped the heavy periods so the mooncup is even better. I won't repeat what everyone else has said about changing it, etc. The only downside I find is that after a long period (about 2 weeks) I get a sore vagina from inserting it too many times, and switch to pads for a couple of days. This will only affect you if you get very long periods though.

If your periods are very heavy there are a couple of cups which have higher capacities, it is worth checking these out on the aforementioned comparison website before you buy.