I do want to learn on the BOV + gag strap.
I would suggest against learning with a BOV. In the early days of rebreather diving you need to constantly practice so the right habits are in place for the day that happened to most of us, when the “unit” tried to kill you. Even if it doesn’t, you must be ready for it to try.
Doing things manually means you get the good habits sorted, banked if you like, such that you can withdraw the effort later.
Typical skills are stage handling procedures such as grabbing the regulator, closing the DSV, removing it from your mouth, breathing from the bailout reg, discovering you’ve not turned the stage on, controlling the rising panic as you’ve not got a breath, turning on the valve, breathing from it, switching back to the loop, tidying the stage hose, clipping the stage on, then pondering what happened and learning the real lesson!
Or just learning that the BOV always works and not worrying about the extra hose even though it may be essential later. Say if you’ve connected the BOV to your diluent, or switching to alternate bailouts, or even to shove a working reg into the mouth of an OOG diver.