Well, yes, the angled exhaust reduces backpressure, and upt the HP a bit, but our engines can't afford to lose too much backpressure. We need the torque!
If you were running a turbo or something, then yes, it'd help, but on a N/A celica, it wouldn't do much for performance.
Looks cool tho. I'll admit that.
A nice, free flowing mandrel bent exhaust would free up more than enough HP, the angled setups are good if you have enough mods to warrant the added flow.