I used to own a jetta with GT25 turbo on my 1.8T. I had a profec A electronic boost controller. I would get that instead of a manual one. Usually, a manual one is inside the engine bay so turning it up or down is quite annoying.
Furthermore and more importantly, it all depends on what kind of setup he has.
Did he get a kit for the k04? They usually come with software since boost in electronically controled from the ECU unless he changed all that or has a standalone (like I did).
I've seen people run that amount of boost on k04's. It's not the best thing to do however getting someking of manual or electronic controller will mix everything up.
Let me know if you have any other questions.