Ok the deal with HKS computers as far as i know is:
FconV
Does fuel only. Now the bad thing with this piggyback ecu is that the standard ecu will still retard timing and add/remove fuel 7.5% either way of the tune put simply. I like to think of it as HKS's answer to the SAFC. Who would pay someone big money to tune an FconV or FconS when you could get an safc done for 200.
FconV Pro
Does fuel and timing and shitloads of other stuff, comparable to a motec, but still not as comprehensive. With thi ecu you have to buy an air temp sensor and a MAP sensor to make it work, an additional $1000 ontop of the ECU. Also it is still a piggyback, leaving the standard ecu to do aircon and demister etc. the fuel/timing is eliminated with a special harness which isnt cheap too. Tuning was very expensive last time i got a quote, it put me off getting one of these ECU's. Imagine forking out truckloads of money everytime you do a mod just to tune your car to it.
-rb25