I've got a 6473-125, Sundance Ozone, Corona Discharge, 240 Volt, 2000 ppm (250mg/h) in a 480 gal HT. The tub gets used at least once a day with the wife and I.
I'm using the BBB method as described on this forum and my numbers have all been in range (FC 3 PH 7.5 CH 200) using the K2006 test...