At my school, mullvad is one of the only VPNs that work since basically every port is blocked except ports 80 and 443 using TCP. Mullvad can use wireguard over TCP on 443, which is very useful.
I hear Mullvad is great but my problem with it is it doesn’t support port forwarding (ProtonVPN is pretty much the only one in the market AFAIK that does).
Not so much a problem if you have high up speeds (like with fiber) or don’t do a lot of torrenting (or are an asshole and torrent without seeding), but I don’t have fiber and have a max up speed of like 15–20 Mb/s.
This was literally the one thing that made me pick proton over mullvad. I know I’m not exactly alone in this, but inbound traffic does matter.