How do outdoor mist-cooling A\C units fare in real-world usage?
For the record, I tried it out myself. I installed the Cool-N-Save system on a 4-ton A/C unit that was scheduled to be replaced in three months. 

After that three month period in the middle of the summer, the positive effects of the system were negligible at best, and probably detrimental. There were no detectible savings in cooling costs nor increase in cooling performance. And after that three-month period, despite using the manufacturer's own anti-calcium system, the calcium build-up on the outdoor unit was extreme, with a thin layer of rock uniformly covering all of the heat-exchanging surfaces, effectively destroying the unit.

So that's a strong "Do Not Buy" from me.