What: Boost Valve
Why: With Rocketchip Stage 2 and Stage 3, it's recommended you use a boost valve to control boost spikes and surges. This also applies to my current custom mapping. For $30, it's good insurance for your $700 turbo. Even stock cars can and do benefit from a properly set boost valve and will keep the turbo healthy for a long time. There is no reason not to have one on every TDI.
What I would do differently: I bought mine from Boostvalve.com ... I would probably buy my future oens from 3Bar Racing. They are basically same, just $20 cheaper.
I purchased mine at Boostvalve.com, but I would probably purchase new ones from 3Bar Racing.