I run 3 of them. 1 for 2-part, Kalk and NOPOX, 1 for Red Sea Coral Colors, and 1 for Red Sea Reef Energy. No problems with them.
I do get air in the lines. I've replaced the tubing, but the bubbles return. I just clear the lines every once in a while. I test Alk daily with a Hanna Checker, so if there is ever a problem, I'll know that day.