Monitoring ORP in my tank gives me an immediate indication if something is wrong with my tank i.e. a fish or coral dying.
Here's my ozone setup, it should be easy to DIY the reactor.
I replaced the MTC carbon reactor with a smaller one that sits in the sump. I also found no need for the separate carbon air filter as excess air in the ozone reactor is carried out with the water.
I use a controller but the ORP has never been high enough to shut it off. Every ones tank is different some have naturally higher ORP levels where ozone would not benefit as much.
What I notice the most besides crystal clear water is darker skim mate (like vodka dosing) and hardly ever have to clean the front glass anymore.
Reefkeeping.com articles on Ozone
http://reefkeeping.com/issues/2006-03/rhf/index.php
http://reefkeeping.com/issues/2006-04/rhf/index.php
http://reefkeeping.com/issues/2006-05/rhf/index.php