I have used a SAK moderator on a 17HMR and no it didn't effect the accuracy once it was zeroed up - There's a lot to be said for the humble SAK moderator. However there is a warning about the SAK moderator on an HMR - If you have a 16 inch barrel (Or shorter) on your HMR I would be inclined to keep a close eye on the baffles as mine (With a 16 inch barrel) started burning the alloy baffles in the SAK moderator in a relatively short time.
As for you asking about would you be better with a dedicated 17 moderator I can't answer that one. I suspect that the sound moderation might be slightly better (But only minimally) however the accuracy should not be any different as long as your barrel threading is spot on.
Maybe someone with a dedicated HMR moderator will reply to your question more helpfully than I can.