best vibration damper 340?

How about the SFI certified fluid damper copies i see on evilbay all the time. Id imagine if its certified to 12,500 rpm should be safe to 6k. Been looking at one of these. Havent pulled the trigger on one yet. Theres one thats $79, and has timing marks engraved into it. Any thoughts on this as opposed to a solid iron damper?

Matt