Be careful Dave, HKS is a slope style of FCD, rather than a solid clamp voltage style. I would not use one.

With slope style, the voltage output from map sensor is being altered (lowered) by the FCD all the time, at a lower scale to normal. (adjusted with the dial) With this style you still retain a fuel cut, but it will activate at higher boost levels.

Example:

0psi standard voltage 2.0v, with HKS 1.8v
10psi standard voltage 3.5v, with HKS 3.0v

and so on.

Problem is this can cause a lean fuel situation, or effect driving for normal driving and low boost, not just high boost.

With a clamp style FCD, the voltage is unaltered from the MAP sensor up until the FCD clamps still.

Example:

0psi standard voltage, 2.0v, clamp FCD 2.0v
10psi standard voltgae 3.5v, clamp FCD 3.5v
12psi (say just below the ECU fuel cut voltage level) 4.2v, clamp FCD 4.2v
anything over 12psi, if the clamp point is set at 4.2v the FCD holds voltage at 4.2v regardless of the boost. So the ECU never activates fuel cut.

Clamp style are better as all aspects of engine running remain unchanged below the FCD clamp point, But with this style you wont have any fuel cut.
(Not a problem if you monitor boost levels with gauge.)

Many of the problems people used to have with GTti such as head cracks or head gaskets (not so much these days with better knowledge) was when using HKS or similar slope style FCD's. They really need to have fuelling mods when using them.