Additional tip for old showers/glass
I love these products, especially the glass one. After cleaning the shower before applying the liquid, I could still see calcium marks. So I cleaned the glass with CLR. I'd recommend this on old showers - clean with CLR first. Thoroughly clean the CLR off, then use the All Purpose Cleaner, and then apply the Enduro Shield glass product. I was surprised by how clean it looked and was, and how the water runs down the glass when showering. All I do now is squeege the glass after a shower, and presto - clean.