I bought the caddis cutter, size 14, and made perfect caddis flies with the first few cuts. It is a beautiful tool and finely crafted. The cutting pad is a nice touch, and I do recommend using it. I used to hand cut my own flies (wings) individually. Now, this takes all of the guess work out. Just be careful to fold the wings even and directly down the middle, before placing it on the hook, a piece of cake! The cut/design allows plenty of space to tie without affecting the wing, and you can adjust the length by moving the wing up and down the hook shank to make a size 12 from a size 14, etc. I make my own wing material, so I don't know how commercial brands will cut. But, I find if you press with consistent, even pressure, the sharp blades will cut perfectly. You can even slightly "roll" or move the blade to each angle to ensure you have cut through each side(front, back, left & right) if necessary with thick wing material. But, even pressure could possibly avoid this, see for yourself! I just bought the tools a few months ago, and have already made about 50 caddis flies. All of them are catching trout. One of my friends, a guide, is using them, and wants all that he can get. I also bought a mayfly cutter, size 18. It works just as well, but is not as versatile as the caddis cutter concerning "streching the size" of the mayfly that you tie.
