This looks really interesting, but I have so many questions. A few important ones that come to mind immediately:

1. What is the user agent that's reported? I'm guessing Firefox, but if there are any indicators that would give it away it's not Vanilla Firefox or a popular fork, this could make you more unique.
2. Are the mods publicly identifiable? Another thing that might make you very unique and prone to fingerprinting.

A core part of being private online is blending in with traffic, so using a niche browser like Zen (depending on the configuration) would make you stand out.

The product looks good, and the privacy policy is pretty good too. Still, it'd be good to understand all the aspects of how Zen prevents you from standing out in the crowd.

I don't know if you or someone else can speak to this. I would jump into their community, but it's on Discord, so that's absolutely not happening.