Mullvad is distributed and funded by Mullvad VPN but it was made entirely by the folks at Tor project. It's by no means "just an ad for a VPN". It's the best anti-fingerprinting browser you can use to browse without connecting to the Tor network. Anti-fingerprinting is very hard hard business. There are a lot of academic research around it that needs perfect implementation. You can tell how much we need that from Google blocking 3rd party cookies in Chrome. It means they figured out a way to track users reliably without the use of cookies and they want to drawn out the competition.