I got one...its cool..your fingers get a little stronger..but after a while you'll just "outgrow" the tool itself. I wouldn't spend more than $5 or so on one..its cool nonetheless though.
they have a whole set now of four different resistances. from 3lb to 9lb, whatever that means. I can get a whole set for 10 bucks just wondering if its worth it of not result wise.
I'd suggest just playing more guitar. It's a REALLY superfluous tool.

This shouldn't be here, though.
Don't tell me what can not be done

Don't tell me what can be done, either.

I love you all no matter what.