HKS can explain what the difference is between the versions, so you should call them. The units are all universal so if the ROM that's in there is not for your car so can replace it with the one that suits your application. You're also going to need the specific harness for the ECU you're hooking it up to.
As far as usefulness goes.....it's useful for a beginner as a way to add fuel when turning up the boost, but a better bet would be to sell all of those units and buy a used HKS VPC. With the VPC you'll have greater control of the fuel, it coverts to car to speed density and if paired with a GCC or a SAFC you could control more fuel and run bigger injectors. The FCON was good in it's time (mid to late 80's) but that time is now long gone. The newer FCON VPRO is light years ahead of the older units in functionality and price.
Daryl