The Loxjie P20 is something I’ve been happy not to comment on to this point, but since you asked specifically I’ll do so …
P20 vs. MCTH … the P20 has significantly better large-scale dynamics, is quieter (blacker background, especially with sensitive, closed-back, dynamic cans), and renders a more stable and expansive stage.
In contrast, the MCTH easily out-resolves the P20, has much better transient response, more realistic timbre, and gains more character from its tube than the P20. Plucked strings or solo piano is a quick way to separate them, with the P20 rapidly falling by the wayside here.
I really found nothing “tubey” about the P20, either good or bad, so compared to “$$$$”, or even “$$”, tube amps, it’s a non-starter. Tube-rolling yielded entirely minimal differences, except in channel balance and transient performance - which, at its best, was still clearly behind the Massdrop unit. Get tubes with good transient performance, properly, and closely, matched (so you don’t lose the benefit of its digital pot attenuator), and don’t spend more than $10 per tube.
If you care more about tone, timbre or resolution, and/or want some “tube flavor”, then the MCTH is the better bet (so is the Vali 2, for what it’s worth). If you are more interested in black-ground, power, dynamics or stage, or just want “balanced because balanced is moar-betterer”, then the P20 is by no means bad for the price.
And, “tube flavor” with the MCTH excepted (which is still limited compared to a real/pure tube amp, like, say, the Bottlehead Crack), the JDS Labs Atom runs rings around both of them when it really comes down to it. There’s nothing approaching “tube sound” in the P20 that would tempt me to use it, on a regular basis, vs. the Atom (or the Magni 3 or even Liquid Spark). And what the P20 might be gaining from being balanced is lost in what are, to me, the most important technical performance characteristics … especially raw resolution.
