You are correct tho; the Duratrax does look like a carbon copy. However, I can almost 100% say that the Duratrax is made with lesser quality plastic.
Havin' driven both, the GT performs leaps-and-bounds better than the Duratrax, as the GT is the purebred (of sorts) racer. The Duratrax, on the other hand, is built more for the basher/entry level racer.