So I have been curious about these for a while, never really took the chance on buying a fixer and seeing what they were all about. Fairly ubiquitous on the eFlay US market, and they tend to go fairly cheap on auction.
Ultimately, I didn't have to buy one...a repeat customer of mine won one on auction and sent it to me for refurb/servicing.
ST-90, ROC-made (the first ones were actually assembled in CZ...at some point, apparently JK subcontracted to china).
This is a pretty good sax, really. I was pleasantly surprised. In general it is modeled after a Yamaha 23 as far as most keywork mechanics and such, although the feel of the JK's keys under the fingers is slicker, more responsive. Body gauge is quite robust, heavier than a student...