I think a lot dependso nthe bike. I had one on the GS and it transformed the bike: the gearbox is made of discarded German tractor parts, and mine was temperamental and rough. On a bad day, the quickshifter would take 2 seconds off every gear change. On my current Tiger, though, I wouldn't bother: the clutch is light, the gearbox is a dream, and there's loads of power a low revs, so there's not a lot to be gained. On a GSX600R, if it were me, I think I'd go for it. I didn't have one on mine, but if I had, it would have have made it easier to shift gears quickly at high revs. And the bike likes to be ridden near the red line