Let me help out here, since I have real experienced with all 3 of them. So rest assured, my opinions are all mine, no conflict of interests, and would not answer your question with question(s).
:-)
Mastersound: I got one real cheap from a lawyer in NJ who cursed it. He let it go real cheap. But the true funny deal was he demo it with an *broken* Audio Physics speakers (broken and dented drivers, absolutely a scene!) --- just enough to show the amp still made sound. Gave away an nice power cord too. I had reliability issue with that amp. Got my local tech guy hands in the air quite few times. Didn’t sound right anyway --- I just got persistent noises and hum. Dumped it into trash in the end as none of my friend wanted it when I offered it for free.
Vaic: I got an "alleged" predecessor of an Ayon SET (I suspect it’s the Ayon Sunrise model) with Vaic badge. Look awfully similar, indeed. That seller from Europe claimed it was basically an Ayon. OK. I had quite a good experience with Vaic tubes before, so obviously, love to try out. My experience was good. Support was non-existence, so whenever it started to acted up (some noises / hum), my local tech’s hands in the air again. Having an 220v unit didn’t help neither. I sold it to a collector in New York City who simply put it on a shell as if it’s an trophy. A happy ending.
Ayon: Now this gets interesting and very long. Noticed the brand was constantly bombarded at various audio sites as ’best of show’, which automatically turned me off. Then got a crazy deal on an Spirit II for $600 or so. I was truly impressed because ....the previous owner who cursed this Ayon Spirit had no idea how to insert an KT88!!! Half the tubes were inserted incorrectly due to broken pins --- no wonder it kept dying on him. I replaced the fuses, put the new KT88s, the unit just *worked*! Not a single burnt mark nor smell, no sign of service, nothing loose, I saw very expensive parts inside, now this is true quality work!!!
I think some posters claimed Ayon is an Chinese product --- and unfortunately, some early low-end models were indeed assembled in China, possibly by Ray-sonic, which copied the Ayon designs (sounds like an Red Rose Music story, huh?) My opinion is simple: If an complete novice keep putting in tubes in the wrong way and didn’t blow the amp up, that says a lot. Who cares!
But Spirit II was just entry-level. I owned the Austrian made 220v Ayon Sunrise SET (thanks to the Vaic experience I mentioned earlier) - under powered for my taste, but the same outstanding workmanship. I had to sell it since the ultra expensive 52B (I think) need to be replaced. Cost a fortune --- almost the cost of the Sunrise itself for a pair.
Then Austrian made US-imported Ayon Triton --- love that amp, kept it for years. Not the most outstanding sounding amp I owned, but delightful and reliable for a long long time. The bias for each of 8 tubes barely moved after 3 years of use. No maintenance whatsoever. How about that.
But Ayon digital products are a different story. I owned Ayon CD1, CD2, CD2-S, CD7 and S-3. Not related to your question, but I’d not recommend the such models in used market.
Hope this helps.