We tested Mullvad Browser in our search for alternative browsers. Unfortunately, it appears that it also didn't support DRM content, which means that it doesn't meet our requirements as a full-featured general-purpose web browser (ditto). In addition, we found their APT repository to be unusually slow and unreliable while installing and updating the browser, which isn't ideal from an end-user perspective.
It's only been around for less than 2 years as an ancillary product in Mullvad's lineup, so we wouldn't be confident in characterising it as "Mature and well-maintained" for long-term support.
Mullvad – as a brand – is certainly more well-known than LibreWolf, but not enough to be considered "Popular and recognisable" by the general public in our view.