I think audio pro's who spend the time complaining about tools that are known, outside their sphere of influence, to work quite well - simply aren't professional enough to admit when they haven't learned enough to get similar results as others, who are .. and UbuntuStudio has had decades, literally, to become that kind of tool. It is used by pro's all over the world to supplant what would otherwise have been a significant financial investment.
It is free, after all, and yet out of the box comes replete with tons of stuff that you'd have to spend, literally, a week getting installed on MacOS/Windows, dealing with licenses, etc.
Zynthian: The latency is really not noticeable - I have a 12 track multi-timbral project running on it right now, it sounds just as rock solid and tight as the 3 rows of 19" rack synths/effects and the half-a-room full of other hardware synths in my studio. It is an extremely capable little box, and its built around existing Linux audio technology - so the point is, it serves as a pretty good reference for how good things can get. Jitter? Haven't noticed it.
Zynthian integrates with all the DAW's in my studio, including UA and MacOS systems, just fine. Its a dream to be able to set it up for remote control over rtpMIDI, for example, and not have to run any cables.
Github issues are a professional way to interact with developers. If I had 2c for every time I heard someone complain about the support they -didn't- receive from Apple because of bugs in Logic, or crashes that Steinberg/Yamaha refuse to fix, or updates to Ableton Live that resulted in unusable projects .. I'd have enough to afford a decent UAD system .. ;)
On the other hand, if you look at the closed issues in the Zynthian github, you'll see so many successful contributions from around the world, making the Zynthian a better product. This is the future.