Time, consistency, etc. My plugs were a cement mixture before and they are doing great but I have to soak them for about 1-2 months before I can sell them. So turn around is a big factor as I can throw these in the kiln as soon as they are dry. Once out of the kiln they are ready to go. People also seem to be a little skeptical about cement even once cured they don't cause issues. For the cement, I have to make the mixture and pour it as fast as I can before the mixture hardens on me. It gets pretty hard when you need to fill a bottle, pour it into molds, and then vibrate them to get out all the air bubbles before the mixture isn't usable anymore. I also can not keep up with the demand, a few of my clients are farms and they go through thousands a month and I am constantly selling out/short on stock.