And as to the OP saying that "why should I pay for metal, theres no optics" I agree. I bought some ebay hong kong extention tubes, $9 with shipping. It's metal, and doesn't allow lens to camera commo, what could it possibly do? I see no need to spend $100 or more on hollow aluminum tubes.
Depends if you want full use of your AF lenses, or if you want to manual focus and lose aperture control. I like the electronics pass through, one less think to worry about and I can let the camera do what I intended it to do. Might as well buy reversing rings if you don't want AF tubes, even cheaper than cheap tubes.
Ever want some fun if you have a 100-400L? Plug in all 3 tubes, then add the 1.4x TC and see how you like your 400mm macro lens!