I actually haven't heard of it but I'm going to look into it now.
Mercari is usually my to go app for items under $300. Be ready for "what's your lowest" comments under every listing. TONS OF FAKES, hence tons of "how do i know its real" customers. I keep reporting the counterfeit bags and they do not get taken down.
I wouldn't recommend them for high-end items, I had 2 returns (both ruled in buyers favor) and it was very hard to reach CS. Bunch of automated emails. With that being said, tradesy is about 60% of my sales, Mercari 20%, ebay 15 and posh 5.