Usual caveat, listen to it in your system before you buy it. Now that's out of the way, I own the Butler amp in question.
Firstly, it's got lots of grunt so no problem in terms of speaker efficiency.
The 6 moons "psychoendorsement" is pretty accurate in terms of the qualities of the amp. It's got a tube flavour along with the ss qualitites of low end control of the bass frequencies (it's not flabby or loose in the nether regions). Delivers good detail and definition. Really nice delivery of vocals, acoustic music, jazz, etc but it can rock as well. Personally, I tend to listen to the latter alot more these days but I still like to crank up a bit of SRV, ZZ Top, Buddy Guy, Stones (old) etc every now & again.
Hybrid amps are nothing new but the design is certainly interesting. Is it snake oil? Maybe, but it's snake oil that tastes good.
Extremely well built, 5 year warranty and Butler has been in the business for a number of years (yes building car amps among other things).
Personally, I think it's a keeper. I liked the idea of a tube amp which didn't require constant biaising, wondering whether the tubes were degrading (obsessive compulsive audiophool behaviour I know), etc.
I bought it from a local dealer who has been in the audio business for decades. He sells mid to hi end gear, is a tube fanatic and has now put a Butler amp into his personal system.
Oh and the blue glow when you turn the lights off is really trendy too.
Again, it's all subjective, but the Butler amp is definitely worth a listen if you can get a home trial.