The mirrors do seem to vibrate a tiny bit more than when on the stock bars, but they also did so before I put on the extenders. I think the the 7/8" bars are more the culprit than the extenders. They are nowhere near as stout as the stock Kawasaki bars. The extra vibration is not a big deal, though.
06 Suzuki DR650SE
04 Yamaha FZ1
90 Honda Hawk GT, 00 Kawasaki W650
79 Honda CBX
82 Honda CB900F