Simply because I work within the construction industry, I have never used anything other than reinforced concrete, and was all set to critise the product that you had linked to as I had never seen it before.
I can't do that though, as after doing a Google search, I reckon that the product could make life much simpler for many people. If you have a level site to begin with, you could well be onto a winner, and thanks for introducing it to me.
