Buddy of mine bought one 3 seasons ago. We tried it out right away and it hasn't come out again. It makes a bloody mess of your birds, yourself and all the area you use to clean them in. There is no structure left to the breast as it tears the rib cages to hell and you are left with a mushy breast with no body that is hard to filet afterwards. The thing is also freakin dangerous, you cant imagine how sharp it is and the serrated cutting edge is downright brutal. If you are not 100% focused on what you are doing you will lose some digits in an awful hurry. It is not something you want to be using while laughing and joking with the guys or after you have had a few sasparillas!!
And yes you have to be popeye to use it for sure, first time I tried it out I did two dozen geese and 15 ducks, I darned near pulled my arsehole inside out....a goose does not pull apart anywhere near as easy as a grouse. If they did we could do the step on the wing thing and save alot of time and hassle cleaning them.
And oh yes, it will not work if you have a bird with a broken wing as you do not have enough back bone left in the broken wing to pull the bird through it. The broken wing tears off instantly leaving you a wingless bird you have to breast in the traditional manner.