The Nexus Tapfire ST-8S20 uses the brake lever as the shift lever (STI style). I like to ride my brake levers a bit so would be worried about unintentional shifts.
I use the Alfine rapidfire levers SL-S500 and they are 1 shift per click but you can shift 3 or four clicks pretty rapidly (maybe all that clarinet practice payed off).
Im not sure if you can use the Tapfire on Alfine but in theory they should work.