My 2 cents
Stun guns = 100% useless against anything. I have idiot friends in the music business who purchase some of the larger capacity stun guns off gunbroker.com and shock each other on a regular basis to show off. I too was tempted to shock myself with one, and unless someone can get this stun gun placed at the base of the attackers neck, a stung gun will do little more than **** someone off.
Tazers, the ones that shot the two probes into the attacker require a bit of aim and a bit of training to use. They look and work much like a hand gun in the sense you have to draw the weapon, aim the weapon and fire. A attacker can always pull out the probes once they are shot into them.
Non lethal defense in my opinion still falls down to a good mace type of weapon. A good alternative to mace is one of those large Ortho or like brand large spray cans of wasp killer. You know the large can that can spray 15 to 30 foot in the air. Make sure you pick a really nasty brand if you go this rout. The warnings on the cans of this stuff for “if you get this in your eyes” reads like a horror story and the manner in which this stuff sprays is like one of those larger water guns. Its just a idea and something that can harmlessly be placed on the night stand that no one will think twice about.