I received a set of the Fasst units free a year ago, and was a non-believer. Best thing I have ever used to dampen the vibration. Don't really care how "free" they were, if they didn't work, they would be in a pile in the shop.
Currently, I run the Pro Tapers, Fasst units, +1 bar towers, and stock rubber bar mounts. Never used the GPR's, but I am sure they are on the same principle. Either way, I am positive you will not regret the purchase. This one is like the reed spacer, a must have.
Next best thing to truing the crank.
Rick