You're getting an STi. Why do you want to do this little mod to it?

 

Currently, HKS doen't offer the F-CON for the STi.

I had an F-CON on a Galant VR-4 for years (as well as many other mods). And while I liked it, I'm not certain I would recommend it for the WRX or the STi. It was expensive and I'm convinced you can get as good if not better results from one of the many other Piggy-back / ECU replacements at significantly less money.

Unless you have a relationship with an HKS shop that knows how to set it up and gives you great prices and service I would go elsewhere. Other tuners such as Vishnu, Turbo XS and Cobb will probably beat HKS to the punch on an Piggy-back or ECU replacement for the STi.

 

One of the biggest selling point of the HKS FconV-pro is that it can run without the MAF sensor.
The engine will be more responsive.
I think the hardest thing about HKS is to find the tuner.
In so-cal, I think SignalAuto and SP does it but it's gonna cost over $700 just to tune it on dyno.
If you are not doing a huge turbo upgrades, I think AFC and those piggybags will work just fine. If you are, then yea F-Con is a good product for it.