Has anyone tried Dermatica’s OTC 15% or 20% Azelaic Acid?

I’m not completely clear how Dermatica is able to sell both 15% and 20% Azelaic Acid as OTC products when every other AA product with those concentrations requires a prescription, but they do, and at really good prices.

Has anyone tried Dermatica’s Azelaic Acid at 15% or 20% concentration? If so, what did you think of the product? Thanks!