I also have the 135mm F2.8 MC Rokkor, and the 135mm F3.5 MC Rokkor. These are extremely underrated and incredibly useful lenses. Tack sharp with lovely out-of-focus. Can be had at garage sale prices. Every Minolta user should have at least one of these. I've had people offer to give them to me, at camera shows. I also had them offered to me at $5😀 How can you possibly go wrong?
The Spiratone 135mm F1.8 MC was just a pig of a lens. But very useful for what it could do, unlike any other at the time it was introduced. Sharpness was pretty decent, depth of field is so thin that it's tough to get much in focus. Much tougher lens to use in my opinion, not saying it is not useful, just more difficult to use effectively with paper thin DOF.