Hi didge333
My friend is Tom Solak from Just Concentrators in Chicago. He says that Airsep and Invacare are the most reliable concentrators over the long haul. His number is 773-685-6966. He regularly sells fully reconditioned units for $475.00.
Dual dialectric ozone generators have absolutely no metals in the gas stream, making the ozone ultra pure and free of ion contamination from metals. This is not an issue for most ozone protocols, but becomes an issue when using ozone for blood protocols like AHT and injection. It has been a hot debate in the inner circles of those in the know about medical ozone for nearly two decades. I personally feel that the benefits of a non dual dialectric unit outweigh the detriment but that's just my opinion. The purists and the best manufacturers in the medical ozone business always use dual dialectric technology.
The POG from Azco Industries(Personal Ozone Generator) on our website is a dual dialectric unit comparable. The drawback with the POG is that it does not have variable output so one needs to use flow regulation to control concentration. It can be special ordered with a ten position output control switch.