Self defense ammo will generally be a seven yard shot or less so velocity drop and mass energy should not be a huge factor.

I think if it does separate into multiple projectiles you are not going to worry about an through and through with an exit wound to worry about colateral targets.

IIRC, glasser safety slugs were developed for the sky marshalls with the idea of preventing cabin wall / aircraft skin penetrations with the goal of preventing depressurization events in case of a miss or a through and through GSW.