I have never seen nor handled a Rockwell (3 piece) razor in person, but the only complaint I have seen in print is that it is somewhat bulky in the head and therefore not easy to shave under the nose with.
I also HAD all 3, i still have 2 Model T's and a Birth Year Slim ( keeper), i prefer the Slim, The 6S was moved on, The Model T's will also probably be moved on.
Get a REX!
The Rockwell 6C in gunmetal is a thing of beauty and I can get a smooth bloodless shave every time with plate 3. The Razorock Gamechanger .68 is equally smooth for me and stainless steel, though not as finely finished.