all it does it remove electronic limiters. The gain assosiated with the JWT ECU is from the boost jets. The boost jets raise the stock boost ~5psi. For every 1psi increase you gain about 12hp. Hence JWT claim that the ECU nets a gain of 60hp.
A set of welding tips and an S-AFC will yeild greater results. Of course if you feel like splurging a little then an electronic boost controller would be better.
The only time you need the JWT ECU is when you plan on making changes to the injectors. Even then you can still get around using the JWT ECU by using other piggy back units available. Best bet would be to go stand alone, that way you can always adjust to accomodate new upgrades as they are added.