I bought a used set, and sold them when I was finished using them. I think they make the process of making the curves on the fuselage sides easier. For the sharper downward bend I used a vise and a 2# dead blow hammer. You just want to be careful using them... it's not a "clamp down and it makes the bend for you" kind of thing. You can put WAY too much bend in the longeron if you get carried away. Gentle squeeze, move the longeron an inch, another gentle squeeze, repeat until it's done. The only thing I didn't like about them is that there is no ridge/step or anything to keep them in place in the vise, but it's not that big of a deal.