The main reason I'm thinking of the GT525's is because Z1 had upgraded 360 degree thrust washers installed for better longevity and are difficult to install if I decide to upgrade injectors later. Not thinking of injector upgrades right now since I don't want the wife's TT to be faster than mine.;)
The stock replacement CHRAs are the most cost conscious but do require more labor to install. The Z1 "rebuilt" turbos are constructed using NEW CHRAs so basically they save the time and labor to install the CHRAs.