Review on Concise Home ozone generator & air purifier - 5000mg commercial air by Renee Chavez

We have had an old heavy duty ozonator for many years and it does the job very well. The only complaint is that the dial isn't calibrated to the scale on the panel. It turns on and off when in the 10 minute position. So if you want it to run for 20 minutes, you need to turn it to the 30 minute position. Update - from 4 stars to 2: After several uses I found that the timer doesn't work at all if it's set for more than 10 minutes. You may feel that there is no resistance when turning the dial. This is very annoying as it has been 40 days since purchase, but I cannot exchange it.