I've used the regular one, works just fine for the somewhat limited use that it has. You could do the same work by hand, but it would be a bit of a pain, so in that regard it's worth the price. The powered one seems a bit over the top, but someone else here may have a good amount of time working with one and have a good opinion on it.
If you have alot of curves to cut a nibbler is the way to go. Years ago, I used mine quite alot to cut out parts for various SCA helmets. You just need a big compressor to run it. Never tried the electric kind.
I know Harbor Freigt get a bad rap sometimes, but I bought their nibbler probably six years ago and it still runs great. Broke the rod once but it was only $5 to replace.