What do you lose in regards to street drivability going from the stock ECU to a PFC?

I read Dale’s FAQ mentioning possible US spec related issues, like fan speeds not always working and losing the EGR functions. But, is there anything else you lose, or does it function identically in every way (or better in cases it seems) to the stock unit? Reading, it’s as if it’s just an unlocked JDM ECU? I’ve got a 94 JDM car, but I’m always leery of aftermarket ECUs taking away from the drivability of a factory effort (they have a lot more money for design and presumably are interested in the most streetable car)

 

If tuned properly zero, though having a PFC properly tuned by someone who knows what they're doing is another conversation entirely. I used to do it, and at this point I don't touch them anymore past helping some locals with diagnostics as I feel there are far better alternatives.

EDIT: By zero I mean zero that you'd notice, there are a couple small things such as CEL etc that do not affect drivability that you'd have to work with.

 

Depends on if your car has to pass emissions testing and be stock.
If not, it is all positives as the AC poor ecu grounding is easy to fix.