Fluiddamper
Yes, I run one. I would say it is worth it. IMHO, there are internal vibrations that WE put in our engines with the mods that we do and the Fluiddamper basically smooths out those vibrations. How do I know this? Because instantly the engine ran smoother and not that I've ever pushed it to the outer limits, but I have run it hard at high rpm and it is definitely a much smoother runing truck with it than without it. I would do it again. $$$ well spent.
Further, I'd bet you that people running serious power like the Garmon Bros. are running it.