I don't have any experience with the one you speak of, but I do with the C&H Reasearch recoil reducer.
The C&H is a machined stainless tube encapsulating the mercury. A nice clean piece.
I installed one in the butt of one of my custom rifles
to give it a better balance. It was exactly 1lb, and that was what I needed. As for recoil reduction... I don't think it made much of a difference..
I'm sure the performance will vary from application to application.