Just for the record:
I've been using Ozone for about 6 years now. I started out with a small 250mg/hour unit and no controller, then graduated to 1g/hour unit back when I had Zilla 2 - the 2000 gallon tank. At a 30% setting on the larger unit, I managed to kill fish (by my-oh-my, how that water sparkled!). That resulted in a controller being bought.
Orp meters (and therefore controllers) are notorious for being inaccurate, with weekly cleanings and calibrations recommended for serious use, which is a LOT more work than I'm willing to put into the hobby.
Currently I run my 1g/hour unit at 50% for Zilla3 - a 5000g tank, directing the O3 into the air feed line of the skimmer. To me, this makes sense, since the purpose of the O3 is to bind and breakdown large organic molecules making them easier to skim.
My RK1000 Ozone unit has dual air driers and is basically self maintaining, excepting occassional air filter changes.
I highly suggest using as little O3 as necessary to removing yellowing compounds in the water and not chasing a number on a meter. You will know when your water sparkles; you will know when it doesn't. Adjust to a setting that works for you and use it.
Oh, note that there is a ton of difference between something like a RedSea unit being fed room air and a commercial unit with air driers like an RK1000. That difference is what killed the fish - the commercial units are just that much more efficient.
Kevin C.