Coming from the reef aquarium hobby into chams.
Ran some extensive tests on home made pump setups, Tunze, Mags, Fluvals, etc... including using brass heads from an outdoor misting system, some irrigation heads, and more.
I ordered a mist king for comparisons with intention to return it based on performance.
Once I started it up I immediately broke down my other experiments.
Runs so well that the next time I need a pump for my mixing station or ATO (auto top off) I'm, ironically, buying the MK pump and modifying it.
I can't see how or why you might have had 3 bad units in a row. I've had mine run dry a few times (once for considerable time) to no ill effect.
Did you communicate with their customer service? If so, how did it work out?
If you're going homemade, I'd recommend looking into the Avast Marine peristaltic pumps. They're workhorses, have a decent push for head height, can run dry for hours, and are relatively affordable, though small. I use them exclusively for a number of applications for my reef tanks.
Unsure if they'd have enough power to push more than one mist head.