Thanks for this, traceroz - I've just ordered a pair, good value at $28 inc postage. They seem to differ from other extenders in that this item comprises a new "foot" that moves the stems and mirrors outboard by 35mm (1.5"), instead of lengthening the stems themselves by means of an insert. I'll leave my 2" dia spot mirrors on, as IMHO they do add another layer of useful wide-angled rear vision...
But - FWIW - I do not seem to experience these mirror vibes that plague some here, it seems. Might happen when I get to 50+ kph!
L of S
I've got the ones that lengthen the stems and have no issues with vibes in the mirrors at any speed. I'm sure the ones you got will be fine too. My old bike may as well not have mirrors is was so blurred at any speed. Night and day difference.