In the early days yes as the gearbox was never designed for them. My mate raced at early R1, a bike not known for a robust gearbox. First season with no shifter one gearbox rebuild, second with a quick shifter 3 rebuilds and that was only an up shifter not down as well which is harder on the gearbox again. Could be me I just don't think there good for the bike longterm.
As has been said a quick shifter is about £250, give me that off the bike and let me spend that on more useful accessories to me, mainstand, hand guards, heated grips etc.