Unfortunately people who have rooted phones, who use nonstandard browsers are not more than 1% of users. It’s important that they exist, but the web is a massive platform. We can not let a tyranny of 1% of users steer the ship. The vast majority of users would benefit from this, if it really works.
However i could see that this tool would be abused by certain websites and prevent users from logging in if on a non standard browser, especially banks. Unfortunate but overall beneficial to the masses.
Edit: Apparently 5% of the time it intentionally omits the result so it can’t be used to block clients. Very reasonable solution.
Depends on what you count as "nonstandard", but various estimates put non-top 6 browser usage at between 3-12% (https://en.wikipedia.org/wiki/Usage_share_of_web_browsers#Su...) and non-Windows/macOS/iOS/Android usage at ~4% (https://en.wikipedia.org/wiki/Usage_share_of_operating_syste....) These also don't take into account traffic on older operating systems or hardware that would be incompatible with these attestations, or clients that spoof their user agent for anonymity.
In an ideal world, we would see this number grow, not shrink. It's not good for consumers if our choices dwindle to just one or two options.