I finished installing a clutch switch last night, so flat-shift is ready to go!
I actually used another brake light switch (they have the same thread to screw into the bracket on the pedal).
If you don't know how flat-shift works, it's a feature in aftermarket ECUs whereby fuel and/or spark is cut whenever the clutch is depressed while at wide-open throttle at high RPM.
It means that you can change gears by using the clutch only, with the accelerator pedal held flat to the floor the whole time. This also means that you can't stuff up the timing of depressing and releasing the clutch and accelerator pedals when trying to shift as quickly as possible.
The main benefit is that in a turbo car, flat-shifting eliminates the issue of the turbo compressor wheel getting slowed down when the throttle snaps shut during a normal gear change, so after the gear change you can be back on full boost with virtually no delay.
The downside is that it puts more stress on the synchros in the transmission.