I own one of these, bought it used a couple years ago. It was a good value, and I believe it had been rated Stereophile Class C. At first I found it a bit lacking in the bass, but perhaps I was expecting a lot from a 100 wpc amplifier. Then I replaced the power cord with an audiophile cord (a Stealth M-7, actually) and it became a different amplifier, with strong, tight bass. (However, the original cord was hardwired in, so replacement was somewhat of a pain.)
I'd say the Studio IV is a good value, given the prices I've seen for it used. If you want to upgrade it, have an IEC socket installed and try using a good power cord.