I have heard some bad things about them from people I trust. I love my fixed blade heads. I really like the Slick Trick. I also use a fob which helps the flight of the fixed blade & I don't have to wary if it might malfunction. I also seen a test on energy lose of mechanical heads verses fixed blade.
With all of that said don't think I'm just a mechanical head basher because I set my wife up with them for a few reasons. First being they were the only head that I could get a hold of that was right for her FOC & second she was using a Wiskerbisquick & I wanted something more forgiving from the contact of her flights. So they do have there place but I demand more perfection from my bow.