A grinder would spin way to fast and possibly not have enough torque to hold up well, in other words the weight of a chicken or 2 may snub out the grinder or burn out the motor. I'm sure something like that would work fine providing you can get a tool with the right rpm and built heavy enough...
The only real manual one I've seen was on you tube a while back it was a 5 gallon bucket with the bottom cut out with plucker fingers through the inside and the guy hung the chicken on a rope attached to the top and bottom so it held the chicken taught then he ran the bucket up and down over the...