The cheapest option, more than enough for my hobby use of mixing synth modules and DAW output. I actually started with searching for an effect unit, and found that this mixer with effects is cheaper than some standalone effects.
Completely transparent, I can't hear any noise or distortion so far. The noise floor when monitoring a microphone is the noise of my room, same as in my other interfaces including Roland Bridge Cast.
The knobs and fader feel solid and smooth. EQ, FX and Balance have a snap point at zero, which are installed slightly off-center. Perfectionists might be unhappy.
On Linux it just works and is recognized as "PCM2902", same as my interface "Behringer U-Control UCA222". It's super old Texas Instruments chip and it has worked great for me.
I can't fully understand routing of internal effects. I can only hear effect if I do all 3:
1) send a channel to "FX" bus (expected)
2) then enable "FX to Main" knob (expected)
3) send the channel to main mix using channel level control (unexpected)
I would expect that if I close channel level and let FX run, I would hear effect sound. But there is silence. But with all 3 enabled I can hear the sound together with effect. A block diagram would be appreciated, but making documentation is additional costs which are cut here as much as possible.
There is a routing limitation as in all Xenyx mixers that the main mix is always present in monitor/headphones. You can't only hear USB/RCA and not the main mix. Would be useful for online videogames or voice calls in general if you don't like to always hear yourself. This unit is for music only.
Careful with headphone output, it can go to harmful volume levels as in most professional equipment. Unlike for example Yamaha who makes mixers with weak amplifiers, which I prefer much better.
Behringer provides us a great service by making decent affordable gear. Don't read "hi-fi" reviews and don't watch influencers.