For starters, the cartridges Taser will sell to civilians have a range of 15 feet, much shorter than the ones they'll sell to government agencies or even private security firms.
Second, Tasers are one-shot devices; if you miss, you need to ditch the old cartridge and insert a new one. If your assailant was within 15 feet to begin with, you probably won't have time for a second shot. Moreover, Taser doesn't sell practice cartridges to private citizens, so the only way to practice with one is to spend $25 a shot with a "live" cartridge.
Third, Tasers incapacitate the target only for as long as they can apply a current. In normal conditions, the battery is good for fifty 30-second "applications," which means you have two options: keep zapping the target every thirty seconds until the police arrive, and hope they take less than 25 minutes, or ditch your $350 Taser and run like Hell, hoping that you'll get far enough to lose your assailant in the (now less than) 30 seconds you have until it cuts out and he starts to recover.
The long and short of it is that Tasers work for cops because they have certain things private citizens do not have. Standard doctrine in Taser deployment is that the officer has to be supported by at least one other cop who is keeping a firearm aimed at the suspect, and ideally another cop or two who can jump in and place restraints on the suspect.
Perhaps most importantly, Tasers can be lethal, so if you, as a private citizen, find yourself having to defend your use of one in court, the same criteria of justifiability apply as if you'd used a firearm.
Frankly, Tasers suck except in a limited set of conditions that typically don't apply to private citizens. If you want to the less-lethal route, I'd say go with pepper spray. The Kimber PepperBlaster (
http://www.kimberamerica.com/products/less-lethal /) is a good competitor for a Taser C2; it has a range of 13 feet against the Taser's 15, it has two shots against the Taser's one, it costs $40 against the Taser's $350, and you can get practice units (which shoot blue dye) that cost $36.