MrsMerton, I have heavy periods, well, I should say "had" - since I've used the Mooncup, not nearly as heavy.
I used to bleed, heavily, for the first three or four days. By the fourth day, it would have settled down to only being full a couple of times a day - before that, I could change it every couple of hours and it would be full.
For the first about four months, I used to wear a pad as well - a belt and braces approach, if you like. That meant if I couldn't get to the loo in time, I had a safety net. I still had fairly hefty period pain at this time too.
But from about the fifth month, that all changed - I was emptying it far less frequently - about the standard amount for a "normal" period - and instead of taking prescription painkillers, I took two paracetamol, taken once - and even those I only took because I was at work, and had to sit down - had I been more mobile I don't think I'd have needed them.
And now, about nine or so months after I started using it, I occasionally wear a pad right at the start if I think I might not be near a loo, but otherwise, I don't bother - and it doesn't leak. I don't fill it anything like as frequently either.
The thought of using tampons - putting cotton wadding in my vagina that leaches blood out of me, causes cramps and that horrible dragging feeling (which has gone too) - I can't tell you how unbearable a thought that is. With a mooncup, I feel far cleaner (no disgusting string, no soggy pad), far healthier (feels like there's a better "environment" internally, shall I say?!) and I'd never go back to tampons, ever.
Try one. If you don't get on with it, I think I'm right in saying you can send it back after three cycles for a full refund. But even if I still had pain, if I was still bleeding heavily, I'd still use it, because it's better than tampons.