GT Tuning stuff is way expensive to get here in the states. And with a few nice alternatives available here, not much incentive to get one from overseas.
From what I've read, Janspeed makes the GT header as well, but it has the replaceable cat which is nice.
I have a GTT header and is it quality, the only difference between the Janspeed and GTT is that the GTT is TIG welded the Janspeed is MIG wlded. Apart from that they are identical. Both the GTT and Janspeed have a removable cat section, you can also get decat pipes for them.