They are really not known in the US, but in Japan and Germany they are well loved.
The slim line integrated amps are insane good. Not many folks in the US know about them, but if you look up the model #'s on YT you will find that they were more high end than the standard sharp offerings. Optonica was Sharps "Elite, or ES" line, like Pioneer and Sony.
I have given up McIntosh gear over the Optonica amps. I ran a MA 6100 for some time and when we moved I was letting some SS gear go, I ended up letting like 8-10 integrated amps go, and kept just the Optonica amps.
I also ran my MC-2105 with an Optonica integrated amp as the preamp.
They just seem to have endless power, super clean soundstage with just the right amount of warmth, they pair well with power hungry speakers and run ice cold.
Some folks dislike the STK chips, but those folks also cant say they have actually listened to an Optonica amp. A STK chip is just micro components, most of them have been decoded now and can be built with full size caps if desired. They make many different drop in replacement PCB's to replace the STK if desired.
No plastic, all metal and glass faceplates, while it looks thin and like 80s cheap gear, in person its built like a tank and just oozes quality.
I am dying for someone to buy that one on eBay. I want to see someone in this forum get it and I want to see their reaction to the phono stage.