The thing with screw on filters, well 10 stop ones is often the camera can't see through them, so you can't easily compose your shot, and autofocus certainly won't work. So you have to set the focus manually, them try and screw the filter in without disturbing the focus, then take the shot. If you knock the camera or the focus, you have to start again. It can get rather infuriating.
I used to have a LCW 10 stop that was great and had little colour cast, but it was a complete PITA.