I use to had one and used it for years. I had the original glass one, and after it broke I bought the glass one. It is great for "polishing" the water.
I no longer use my diatom---I use the micron filter in my HOT mag==easier to use.
The micron filter comes with the filter unit. You use the regular filter most of the time, and switch over to the micron filter just to polish the water. Instructions are in the box.