Funny you ask. I have been hearing alot of good reports about the new BowJax crossbow kit. I picked one up tonight and installed it on my Excal Vortex. Took a couple shots in the garage just to try it out. I must say that i did feel a significant reduction in vibration and less of a "twang"(you excal shooters know what I mean).
The kit includes 2 limb dampeners, 4 string silencers and 1 bolt retention dampener. I did not like the rentention dampener on the Excal. Because the spring sits low against the rail on Excals, the dampener was rubbing on the arrow, which should slow it down a bit.
I need to get it outside and do some more shooting but my first impressions was that it helped.