Greg Koch is an amazing guitarist, that is a fact. As far as the amps go, they are not as boutique as others are. They are PCB construction and the parts are largely sourced out. I.E. the chassis, supplies, and other parts are likely made by a third-party company and the amp is just designed and assembled at Koch's shop in the Netherlands. That is right, Koch amplifiers are from the Netherlands. They started in 1988 if I am not mistaken, so are pre " boutique " era and have been mostly limited to the US due to distribution hang-ups. Interestingly enough Greg Koch has NOTHING to do with Koch amps. Greg was born in Wisconsin USA in 1966. Dolf Koch of Koch amps fame was born in 1948 in the Netherlands of course. Dolf was still in a technical school in the Netherlands when Greg was born. In either case, it seems msome tie Greg and Koch amps into a singular entity; they are not.
That being said, despite the positive reviews and recent resurgence of Koch amps in the Americas, they just aren't that common here yet. My only warning about them is that they are PCB based amps, so when things go wrong, it is not always an easy fix, they are also priced very competitively which means despite their high level of quality assurance, they are still affordable to produce and make money from. The lack of distributers or shops that can easily fix them or deal with warranty issues is not going to be as easy as walking to the guitar center. If you can get one to listen to yourself, I say use that as your guiding hand, if you are looking to buy one sight unseen, well I would hold onto your cash until you can. They sound great and have their thing going on, are mostly borrowed circuits that provide the flavor of their inspiration, and are well made. I just like amps that I know I can have easily repaired by a tech and have US-based offices.