The only problem with that is immobilization of the attacker's legs with a pelvic shot doesn't prevent him from firing a gun. While it can be an effective target, the context of the situation is important.

I knew a paramedic who told me an interesting story. He said he responded to a call where a guy on PCP was hit by a car while walking. The impact broke his femur. The only thing on the guy's mind was that he couldn't figure out why he couldn't get up and walk away. He had no clue his leg was broken. If such a person were attacking me with a gun, I wouldn't count on a pelvic shot keeping him from shooting at me. If he were attacking me with an impact weapon or knife and his pelvis was the only/best target available, then it could work. Context is important.