personally I reckon that they're too big. but I've never used one just done some research looking at compressor maps etc. can't remember at what RPM a subaru makes full boost..but lets say it's 2500 RPM.
its a 2 litre engine and more efficient than an a series...so its hard to imagine the turbo on an a series making much boost below 4500 RPM...of the top of my head...my calcs suggested full (7 -10 psi)boost at about 5500 RPM. with plenty of surge below that.

You must remember that the swift engine is more effient(ie flow more air) than an a12 and this probably helps make this turbo more viable on a swift.

I've seen excellent results from WRX turbos on a 1300cc Suzuki Swift engines. Go for it.

I have a friend who wants to sell me his turbo from his 06 Subaru WRX. He just got a bigger one. He says it's made by IHI and it's a TD04-13G. Does anyone know about this turbo and whether it's too big or ok for an a12-a15? It's both water and oil cooled.