For water ozonation, it is generally considered safe to use ambient air ozonators. This is based upon people like Ed McCabe and various ozone experts. Not sure what Pressman has to say about it. But then again he has a vested interest in medical grade ozoantors. I know I used a cheapy ambient air ozonator for water for a year and recognized benefit from it. Peru who sometimes posts to this forum also has built ozonators and he has said that using NoX detecting equipment he has seen little to no NoX in some of the ambient air ozonators.
Clearly for insufflation and transdermal application, medical is a must. But I would still maintain that the ambient air ozonators are fine for drinking water. There are a lot of folks out there that are just barely starting to understand the benefits of ozone and they would never pay $300, $600, let alone $3200 for a medical grade unit just to see if they like it. But I've seen over and over, people who get a little $50 water ozonator and gain tremendous benefit from it. Suddenly they want to upgrade to something better that they can use to do other things like insufflation. Ozone is so good it's a natural progression. My guess is many of your customers have already owned one of these little units and they likely never would have purchased yours if they hadn't.