Both have the same purpose and effects, but differ in the way you use them and their legal status. A tazer is a stun gun that you can operate over a distance; you can shoot its electrodes as far as 15 feet and more, hit the subject with, so he/she starts twitching losing all muscles coordination. A tazer is considered a weapon by the law (not but sane people), you need to be licensed to carry and to use it.
A stun gun has the same effect, but its electrodes are fixed, therefore you need to be in direct contact with the subject. A stun gun is legal, anyone can carry it, in fact it is recommended to do so. In my opinion, it is stupid to deny a 80lb little old lady the ability to protect herself from a distance. Stun gun is good, better than nothing, but a tazer is what she should be having.
Harming/damaging another person
Both tazers and stun guns do not have damaging long term side effects. They scramble the electrical signals that the central nervous system sends constantly to various muscles. It is something like a lightning can scramble your car’s radio menu for a few minutes. However,t you can really mess up a person that carries a pacemaker, and/or has heart problems related to heartbeats regularity and such. There might be other dangers, related to other medical condition, that I’m not aware of. Mathematics Relax. Don’t let your eyes glaze over on me. Its just to explain why gazillion volts like 3 million volts delivered by a stun gun do not fry the guy on the spot. That's because a stun gun uses a huge voltage but has no current, hence has no power.
Power is measured in Watts, like when you buy a light bulb it say Watts on it 40, 60, 100 watts. Watts are voltage multiplied by current. Tension is measured in Volts; it’s like how big is your tank of water way up the hill, 50, 1000, 1000.000 gallons? Current is measured in Amperes. It is like how big is the diameter of the pipe that you will use to drain water from that up the hill tank.
Power = V (the tank in volts) x A (the current in Amperes), let make more scientific... P=V x A
A stun gun has a huge V but no A, well almost none. The huge V is necessary to create that darn spark.
A stun gun is practically useless in Alaska but works like a charm in Florida. This is so because electricity does not go well through cloths, and it will probably not go through a plastic wind breaker at all. A tazer on the other hand shoots prongs that are like nails and it will penetrate most clothing and touch the skin.
Rule of the thumb; the higher the voltage the more chances for the jolt to pass through insulations, such as clothing, especially if the guy transpires a little bit.
The stun gun is the poor, not licensed man tazer. A very high tension might help, but you still have to touch the guy in a spot that is not insulated too much. Some stun guns have prongs pointing forward, like nails, which is very, very smart and good indeed. Bottom line: you should carry one.