Yes, just in case this slipped by, the Hassy does have a unique little "clippy" thing that attaches the strap to the body. I went through the whole "what strap for Hassy" some years ago until I got fed up and just paid the $60 for the OEM strap. I wasn't aware that Op-tec even made straps for Hasselblad. That's what I get for not looking a little more! FWIW though, the expensive Hassy strap is a good one, albeit a stretch at $60.
If you get an Op-tec and it's good, please post on it. I'd be interested to know, if not anyone else.