I still say that the Grim Reaper is probably the best mechanical head out there and they kill very quickly, but I do have a few issues with them.
First, I was extremely disappointed with the blood trails I got even though it's a 1 3/4" head. It kills quickly, but the blood trails are poor. My real reason for shooting them was always for the extra blood a bigger head would deliver. That never happened. That's probably because of reason two.
Second, they're not very sharp and those little blades are really hard to get super sharp. Well, I actually never managed to get them super sharp.
Third, I usually only got one shot and then the blades needed to be replaced.