I have been running the Extra heavy ones for over a year, won them at a rally as a door prize.
I never had an issue with vibes on the C14, but I must say the HVMP's are a real nice product, and did smooth out the feel slightly...if that is how to explain it.
I like the fact they increase the grip area length, and offer me an alternative hand position for changing up to on long rides...coupled with the fact that they will never corrode from hand perspiration like the originals, they are a winner in my book....good product from good COG'rs.