Tasers are legal to carry, but have a very short range category. They all have a small ammo capacity, usually 4 rounds.
If he decides a melee stun weapon is better, then opt for shock gloves or shock frills* instead of a stun baton; both use Unarmed Combat for the attack test and can discharge up to 10 times before their power source is drained.
* - Requires the nonconductivity armor modification to be used.