From the FAQ page (https://leta.mullvad.net/faq) :
> However, Leta is useless as a service if you use the perfect non-logging VPN, a privacy focussed DNS service, a web browser that resists fingerprinting, and correlation attacks from global actors. Leta is also useless if your browser blocks all cookies, tracking pixels and other tracking technologies.
In other words everyone can benefit from it. I don't know any browser (not talking about obscure browsers like lynx) who can completely resist fingerprinting.
Mullvad makes a fingerprinting resistant browser. It uses tricks like displaying the content inside a smaller window to mimic popular laptops and phones.
https://mullvad.net/en/browser
It's not perfect (it's firefox based so that already sticks out) but better than could be done otherwise.
Using an obscure browser that is not hiding its user agent is arguably worse for fingerprinting.