I have two of Surveyor's sheaves and it makes a big difference. Also both sheaves are able to turn on mine so it feels almost like the difference between a ring and ring saver and a pulley saver.
I agree Huff, bought the original found it heavy and clunky but liked the concept. Sold that and have the homemade light aluminium one that my friend gave me. Will be buying the new improved version as soon as Luke has them in stock. Like the rolling sheave addition and the fact that ISC is making them.