I thought he meant "taser" iniatially....then I got it. Actually I believe they are legal depending on where you live, for instance I see them at gun shows from time to time here in Florida. I also know we had them at the machine-gun shoots up in Hernando County, just couldn't use them because it was always too dry (high fire hazzard).
Are they "worth" it......
Cost isn't too high on 'em, or used to be. So monetarily, yes.
Fun to shoot at night.....HELLS YEA! So long as its not an issue setting the brush fire....
Worth it in a tactical, civilian situation..... erm, no. Not even if you have your tax stamp/licence for full auto small arms. Also tactical/civilian is an oxymoron....kinda like military intellegence or government efficency.... Two words combined that just cancell each other out.

-Bill Liptak