I have based my En + GTD system on TSW (The Secret Weapon) and am very happy with the result. In support of Grumpy I have simplified the structure a bit. (Just one Notebook) but the who, what, where, when format makes good sense to me. I have spent some time on their forum and can say that A) I hate their forum software, but They just want to share what is working for them as a group. The majority of their company uses the system. EN + GTD is intensely personal, any pre-made structure you pick up needs modifications to "work for you". I started with Dan Gold's structure, found TSW and now I have a hybrid design that I really like.
I would love to see TSW gain some traction and become popular because it deserves it. Don't worry, nothing fishey going on they just love the system.