free fuel cut or HKS FCD can lead to other systems on your supra to recieve false signals and therefore operate incorrectly (see mkiv.com under "TECH"). the BCC gets the signals much closer to what they should be ... i have a new one for $90 if you want it. email me at [email protected] if interested or if you have any more questions.
Apparently you didn't read it too carefully. Here's the relevant quote:
"The HKS FCD and the FFCD either modify or eliminate this feedback to the ECU and put the EBV in fail-safe mode which fully opens the EBV at only 2500 rpm. This causes a severe drop in boost at the transition between single and twin turbo operation, some owners have seen boost drops to as low as 5 psi before the #2 turbo comes on line, then sudden spikes as high as 17 and 18 psi that will really make you think that you have more power when in fact you are killing your midrange power and then suddenly bringing back full power. While not damaging to the turbos because you are providing plenty of prespool to the #2 turbo, it really masks the true potential of the car, and makes the car harder to drive smoothly."
So the FCD actually gives you more prespool than necessary, causing a loss of lower mid-range power/torque. Go with the BCC!