Ok, TMI post so scroll on by those who are squeamish.
I have very heavy periods. Lots of clots. When I use a mooncup, I have to empty it every hour for the first two days of my period.
When I changed from using tampons to using a mooncup, my whole period changed. I used to have heavy flow for 7-9 days, no lighter days at all. With a mooncup, it changed to really heavy for the first two days, then lighter flow for 3/4 more days. When I changed to period pants, it has changed a little, bit I have noticed that rather than my flow changing, it’s more that I lose blood when I go to the toilet (and I feel the need to go more often - oddly roughly in line with when I used to have to empty my mooncup) so although I do obviously lose blood into the period pants, there is an awful lot that goes straight down the toilet. And clots are often wiped away.
I drive a lot, and cannot access a toilet for up to 3 hours, and in those circumstances, my period pants hold out. Yes, I c an feel the blood/clots/whatever leaking into my pants, but just the same as when using a pad. Oddly enough, I always hated using pads - went straight to tampons from my first period, and only ever used pads post birth (and couldn’t wait to get back to tampons/mooncup once I’d switched), but for some reason, this feels very different. The pants are definitely a lot more comfortable than disposable pads. I have recently trialled reusable pads in case my dd2 wants to try those out (so I can truly know if reliable) and again, they are so much more comfortable.
Period pants really do stand up to heavy periods and clots.