Don't get me wrong, because in principal, I like this idea and it seams very good, but ..... What would this BB gun give you that dry firing won't ? It my even take away from your dry firing practice.
80% of gun training is to master the trigger (the rest (20%) goes to grip, sights and posture, that you can do with the real gun), with most of it happening during live firing, when we all work hard not to flinch.
During the dry firing training, you get acquainted with your real trigger and its very specific attributes, the slack, the wall, the shot, that you can only get from the real gun, as the BB won't feel like the real thing, even so it might be very close. Don't forget, you are working to develop very acute and very fast muscle memories with one specific gun, you don't want to develop those muscle memories on a very similar gun (the BB), it will end up throwing you off.
The dry firing practice will also let you train in sight acquisition, and the BB cannot substitute the magazine change's training (over a bed is very helpful).
Same for gaining speed from shooting from the holster, your real gun will also be a better tool to train with, as the BB is 26 oz vs 32 oz for the real gun.
Concerning the recoil management, it can only be done with practice with live ammo, their is no way around it. Each gun is too specific of the way it comes back to target.
My 2 dineros includes the following suggestion:
For the $90 of the P09 BB cost, get yourself the Lee single stage press and start reloading. You will cut your ammo cost by almost half. How do you think we can all afford shooting that much

we just reload a S&+t load of ammo.