You can buy O2 tests for aquariums, about the only way to truly now. Setup two tanks with the same water, same surface agitation and add the oxygenator thing and see if there is a huge difference or not.I would like to know how much oxygen dose that thing releases, air we breathe has only around 20.95 oxygen so that is what we pump in with air stone, plus 78.08% nitrogen, 0.93% argon, 0.038% carbon dioxide, trace amounts of other gases, and a variable amount (average around 1%) of water vapor.
I think that's what on ebiken shrimp rack I saw.
How often do you need to refill the thing and what size do you haveI am using it, but cant tell you if it is really making a difference. Also have 2 sponge filters in the same tank
I do have the peace of mind that if the power goes out the water will still have plenty of O2. Since I have it in my tank with BB and tibees, its worth the $30.