That the unit's housing and enclosure are impervious to the corrosive effects of ozone-inferior metals or materials. Such materials should not be used. Natural rubber for example will deteriorate in the presence of ozone very quickly. That the method the manufacturer uses to rate the amount of ozone produced is comparable as is based on a known flow-rate. There are two methods in use to measure ozone output.
Most manufacturers use a chemical titration method that gives an incorrectly high rating.
That the airstone and check valve are made of ozone resistant material. That the warranty is comparable. The SOTA's WOZ3 has a two-year warranty. Or, can it only be used plugged into an electrical wall plug. SOTA's WOZ3 has all three of the above features.