$600 list price in 1975. Ads declare a full-logic decoder. If the internal decoder is a 1974 or 1975 designed unit it may be true full logic. What were there... 3 or so types of logic that were labeled full-logic??
I had one of these for awhile. One of those lucky thrift store finds. It was well-built, rugged, reliable. Going on memory alone I say it decodes comparably with my current stand-alone decoder, a Sony SQA-2030.
My personal preference is for Sansui's Vario-Matrix for synthesizing quad from stereo. Those with the Tate's etc. usually say it's the best unit.... if you can afford it!!!!!
For the masses without the funds the later Sony SQ decoders are okay.... the quad effect is there with encoded material and they do synthesize quad from stereo.
No data on output but I believe my unit was around 25 watts per with low distortion. Of course, mileage may vary depending upon the condition of the components comprising the unit.
Sadly, the old Sony magazine ads concentrated on fluff vice facts so I have been unable to garner much info. The Orion bluebook of audio gear likely lists some power outputs, etc. especially an older book when the quad stuff wasn't as old.
What's laughable in the Orion guide are the prices.... less than $100 for a primo QRX-9001!!!!!!!
Depending upon the price and condition the Sony can be a decent unit. I was thrilled with mine, especialy for the 20 bux I paid for it. It functioned fine for 4 years before sumpthin' went bad and distortion grew. I tossed it since I didn't have the skills to fix it or the money to pay to have it fixed.
Of course, what is considered good or not is a subjective judgement call. I would rate the SQR-X750 receiver series as good but not great.