I can understand wanting something lightweight, but I'm not sure I'd like its functionality. I've used the SKF and it's OK although I didn't like the material.
I've got a Logitech Combo Touch case for my iPad Air 4. It's 1.27 pounds (so 576g). Its functionality is solid; the keyboard is very comfortable, and I never think about the additional weight or slight increase in size. If you do find something lighter, I'd wonder how comfortable it is to type on, its stability, and longer term reliability.