Bob Rawle Does alot of mapping on Legacys but has to fly in from the UK, he mapped mine (coincidently if you have an auto I have a mapped ECU for sale )
TDP map them too I think, ask Dave from STiTuning
Pros, can use any Fuel you want, may gain a few BhP depending on mods but the main thing is you won't blow your engine up! I don't really think you have any choice if you want a jap import other than to remap it
Cons: you'll be about €5-600 poorer that's about it