Correct on the quickshifter description of operation.
Air shifters can drop .2 to .3 off of your et's in drag racing.
Although, the AMA Supersport class will prove you can actually shifter quicker without one. The class allows any bike 1000cc's or above. These guys are running stock length, stock height, no major engine mods as they are not permitted, just a few bolt ons like exhaust and utilize stock clutch systems with very minor mods.
Section 4
They consistently run 9.1's with the top riders (Rickey Gadsen, Joey Gladstone, Jeremy Teasley, etc.) running consistent 8.90's all by foot shifting.
They keep their foot under the shift lever pulling it up the whole time and fan the clutch lever everytime they want to shift. The second they brush the clutch lever it is enough to allow the gears to change. No chopping the throttle, no loss of RPM's. In some instances they reverse the shift pattern so all they have to do is hold push their foot down instead of pulling it up.
With an air shift a delay must be added in order to kill the engine for a shift. Some kill the spark, some kill the fuel and some do both. The minimum time of kill to shift from 1st to 2nd reliably must be around 50 milliseconds. After that you can actually reduce the milliseconds for each progressive gear as it gets easier for the bike to shift.
Bazzaz sells a unit that allows you to tune the delay for each gearshift. MPS has a box with one adjustable range for all the gears and also program your stock ECU to activate and airshifter.
I can't comment on the electric shifters as I have no experience with them.
I love this class as it is as close as you can get to stock bikes drag racing possible and they are the best riders on the planet.