The point of the quickshifter isn't so you can shift without the clutch, its so you can shift without releasing the THROTTLE. Clutchless upshifts are possible on all vehicles with fully synchronized transmissions like we have in our motorcycles. A quickshifter minimizes the reduction in engine power to allow a smooth shift without requiring user throttle input.
You don't need this for vehicles on the street, but if you do track days and may want one - some of them are user configurable for the RPM required to activate them. Example: on my track bike, a CBR600RR, the quickshifter doesn't do anything when shifting below 8000 rpm, to prevent stupid fuel/ign cuts while simply moving the bike around normally. Once you're above 8k revs, moving the shift lever to shift up a gear causes the cut out.
I don't know about OEM quickshifters but mine is not really useful except for full throttle upshifting (like on a straight away), when I am short shifting to optimize a particular set of corners not at full throttle I still use the clutch to make sure its smooth.