Hello, thanks for updating!!
(Windows user) In a new play-through it seems restraints are treated as "shared" in the store (they can't be bought for each model like clothes, and can only be purchased once), but treated as "individual" in sessions (so, only the model selected when they were purchased can use them in any session).
This can really limit session selection. It would make sense if they were "shared" in both settings, or even "individual" in both, but this is a little frustrating. I have to switch models and check their restraint inventory before accepting commissions.