When I use a tampon on a heavy night, what happens is that it gets full and then the blood sort of trickles out along the threads. The clots still get caught in the tampon. But when I use the cup and it gets full, it trickles out through the little holes, and it doesn't get concentrated along any threads so it runs a bit more. That's what happened last night. I did use a pad, too, but unfortunately not the big night-time pads. So when the cup got full, I some of the blood ended up on my panties rather than in the pad. Fortunately I woke up around 4.30 am and discovered this before it had spread to the bed. So this was the second night of getting up and washing panties (and also the floor towel), and then fixing the cup, and getting clean panties, and putting in a larger pad just in case...
So, after last night, I have to say that I would prefer using a tampon at night. The max size tampons do last almost a full night, and the cup just doesn't, not during the first three or four days of my period. Tonight I'll have to set an alarm to get up about five hours after I empty the cup before bed.
Another downside is that with the tampon I usually feel when it starts to get full. With the cup, I just don't feel it. Of course the upside is that I don't feel it much at all, which is way nicer than the pain I get from the tampons, and it'll be very handy when I go to the gym or if I want to go swimming when on my period. I think it'll be good when I go riding too, though I won't get to try that until next month. But since I don't feel any difference from a full cup or a half-empty one, I tend to go check on it quite often. And taking it out is painful still, though I've gotten better at finding the nub. It's just the final pull when the vacuum lets go that is quite unpleasant. The pain does go away after a few minutes, but it's significant during that time.
Oh, another thing. A friend of mine said that she'd heard that it's bad to use the cup if you have endometriosis, like I have. I checked on that, and as far as I've been able to find, it's based on old science that has since been disproved but that unfortunately some doctors still believe in. There used to be a theory that endometriosis was caused by menstrual blood flowing "backwards" instead of running out through the vagina, and the particles of endometrium that came along with the blood would get stuck and become endometriosis nodes. However, this has been disproved, for two reasons - firstly, that a lot of women have retrograde menstruation without having endometriosis, and second, that people who have never had periods can still get endometriosis (e.g. infants and some men who've gotten it after hormone treatments for other diseases). So that's not an issue.
So my experience of the moon cup so far: It's comfortable, but not quite reliable, especially not when you've got a heavy flow. It's a bit tricky to handle at the start but you learn quickly. It's more of a hassle to change it than to change tampons, so with a heavy flow it might not be useful when you're working or just out and about and maybe can't get into a good place to change and wash it. I'm not going to stop using it, but it can't be my only option.