Considering oil in the intake is potentially fatal for a motor (I'm proof) I'd say a catch can is very important on high HP turbo cars.
However, a poor catch can may be worse. I've always been told two catch cans is the *only* way to be sure it's right, but there are also considerations with hose size and plumbing configuration that make the difference between blowing up a motor and cleaning the oil out of the intake. Since I never actually figured it out on my car, and ended up just going to a massive breather can, I'm not willing to comment on what's "right".
Chances are all the "kits" out there are just doing catch cans lip service because 90% of the people out there don't need 'em. And for the 10% that do, they're not messing around with "kits". I tried the Perrin kit... and it didn't work for me. I tried like 40 different configurations to try to get it to work (including adding a second can)... but by the time things were "all set" I think my ring lands were so far gone that *no* catch can could handle the blowby pressure my crankcase was seeing.
So, I'd say, get the opinion of a professional on this one, I don't know anyone in the club that can answer this one in a manner that would be "right". But if you have an hour or six, I'd be happy to sketch out the oil breather system on the WRX, the STi, and hybrid WRX/STi motors, and list all the possible known methods for catching the blowby oil in them. Bring beer and a whiteboard.
