The gripper does an excellent job. I have a 72" metal halide / PC / VHO combo hood made of glass and aluminum (pretty heavy) hanging from three single cables as the ones shown and never had it fall or slip down.
If you will be rising and lowering the hood very often (Like for maintaing the tank) I will suggest to attach hooks on the hood and on the ceiling in addition to the hangers so you can temporary attach some small chains to rise the hood. You can just un-hook and remove the chains after you are done. This way you do not have to readjust the height and the gripper or cable will not wer out.