Have just fitted 40mm extensions From Cosmo moto (posted from Thessaloniki and arrived promptly, similar to previous pic) AND have added a pair if cranked extensions purely for extra height as I'm tall from the a** up; the crank is facing forward as the straight extensions provide sufficient width. I've yet to give the set-up serious use so cannot comment on vibration. The further forward position facilitates use of mirrors with less head movement required to obtain a view to the rear.
FYI Cosmo do quite the best SatNav mount I've yet to see, my Garmin is now positioned immediately above the dash & close to the screen of the Tracer, again just a minimal eye glance away from the road ahead.