Less-lethal ammo should only be used for professional use, as in law enforcement, where there's still a weapon with real bullets trained on the aggressor. Having it as a home/self defense load is just an all around bad choice.
Pattern different loads of buckshot, see what works best for your individual shotgun and needs, and keep it loaded with that.
I volunteered once to be shot with a less-lethal slug in the upper thigh. It hurts like hell, but mostly it enraged me to the point of going after the instructor, intent on removing his testicles with my hands. I was able to catch up to him and grab the collar of his shirt before he jumped over a table. Now if you add in the fact that you might be dealing with someone on drugs with even less pain reception, and will actually kill you, you're gonna be in a bad spot. Especially if that adrenaline kicks in and you're standing there pulling the trigger wondering why the gun isn't firing.
A partner of mine took rubber buckshot to the gut and had basically the same reaction.
So, to recap: rubber bullets in the force continuum for professional use = good. Rubber bullets for self defense =bad.
Stop trying to make things more complicated than they need to be.