I have not use but i have a friend who used it before,here's what i think,
1.It is engine specific,the mapping inside is for certain engine and not advisable to be used with another type of engine.
2.Since it is engine specific,it is compatible to the engine it is set up for.
3.Result of course better than stock,this is a piggyback not standalone,cause it is plugged between the ecu and sensor (from the looks of it),normally PFC F-con is coupled with HKS GCC to tune the air fuel ratio,like SAFC.
I would suggest u use e-manage instead.