The Stun Gun
A stun gun must be used on contact and requires that it be held forcibly against the skin for several seconds, preferably on the neck.
Therefore a stun gun requires that you overpower the subject or take them by surprise for it to be effective.
Stun guns rely only on pain to be effective, and many people are able to withstand the pain.
There is a very real danger that the subject will take it away from you and use it against you.
In summary, although the stun gun is inexpensive, it is a primitive and usually ineffective weapon.
TASER Weapons fire from a safe distance of several feet away so you never need to get close to the subject.
Two electrodes connected by wires are fired that penetrate the skin, and 50,000 volts of current flow through the body
completely disrupting the central nervous system. It is 99.9% effective and incapacitates for several minutes.
The current is even effective through clothing, and there is no danger that the current will affect you.
When equipped with an integrated laser sight, there is also a substantial deterrence factor.