Think of it more like this
A blow off costs around $275 after you buy it, the flange and have it welded on your pipe, even more if its an HKS SSQ. A turbo rebuild is around $350 and I have yet to hear any of the turbo specialists say that they have rebuilt a turbo due to the backpressure after the TB closing on a GN.
Save your dough, most guys end up upgrading turbo's every two years anyways so no worries.