I don't think frangible ammo is banned in any particular state (that I know of). They are NOT more deadly than FMJ or JHP rounds due to lack of penetration.
Frangible ammo is used predominantly when shooting steel targets or training in a shoot house (training facility for LE/Military) because the projectile (bullet) disintegrates (fragments or breaks up) upon impact instead of ricocheting back at shooter. Some indoor ranges insist on frangible ammo for rifle shooting to prevent damage to the ranges backstop.
Some frangible ammo is able to be fired at steel at near point blank range and is beneficial for training for CQB situations. Frangible ammo is sometimes referred to as Glaser rounds.