Good luck, tried ordering twice and neither shipment ever made it 
I have two units. Gave one to my father, he will be my control. (Running with no extras except Hydroguard)
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The O2Grow is not pseudoscience–it is pretty basic chemistry that has been around since the 1870s. When I made electrolysis units as a kid in chemistry camp, we would use model train controllers and wires to collect hydrogen and oxygen in test tubes, then blow them up with a match when the teacher was distracted.
I think the skepticism expressed here comes from a misunderstanding of the chemistry–this unit is in no way an air pump. The controller unit is simply an AC/DC converter (. AC power is connected to the controller and the wires that run to the emitters carry 12V DC-- positive to one plate and negative to the other. The gap between them is where the magic(chemistry) happens. 
When direct current (from the controller) is passed through an electrolyte (our nutrient water–it won’t work in distilled water for this reason), a chemical reaction occurs at the electrodes (the two plates of the O2Grow emitters). The electricity that passes from one plate of the emitter to the other decomposes the water molecules into hydrogen and oxygen. This is why gas bubbles begin to form on the electrodes-- the oxygen ions, with their negative charge, will be attracted to the cathode plate, and the positive hydrogen ions will accumulate on the anode plate. Much of the oxygen generated is held in solution by the water, thus raising the DO of the nutrient solution.
It is true that there is only so much oxygen that water can hold. The maximum carrying capacity is directly linked to the temperature of the water–cold water can hold much more oxygen than warm water-- which is why keeping temps low in our rDWC systems is so critical. For this reason, I would not recommend this product unless you can keep temps low enough (68F or lower) to realize the increase in DO that it can deliver.
It is false that the amount of oxygen in the bubbles depends on the size of your pump-- it depends on the percentage of oxygen in the air you are pumping (you could hook pure O2 up to the inlet side of your compressor, but that carries some significant safety/expense concerns). That is the beauty of electrolysis: you are actually generating oxygen without having to buy it in a tank.
I have no affiliation with O2Grow-- I purchased one of their 20 gallon models for my r-DWC setup. My O2Grow controller is plugged into a relay-switched AC outlet controlled by a RaspberryPi which gets inputs from an Atlas Scientific Dissolved Oxygen (DO) sensor. Any time the system drops below 8.0mg/L, the O2Grow will turn on for 30 minutes. Usually, this results in average DO levels of 12.0mg/L in my system. I think you definitely need a DO meter to get this product working right for you-- you could just follow the manufacturer’s recommendations for daily run cycles, use a simple timer and probably get good results, but to minimize energy use and maximize DO in your system, you’ll want the feedback of a good sensor.
I found this product because I couldn’t understand why we all use air pumps to oxygenate our nutrient water. O2 is only about 23% of the ambient air, so pumping air is a very poor way to oxygenate water. Also, the air we are pumping in often comes from our grow space and heats the water, which decreases its maximum carrying capacity for dissolved oxygen. Lastly, as the OP notes, an air pump is loud and inefficient-- the O2Grow is silent. My prior setup used a 50W compressor pump, and ran 24/7–36 kwh per month! The O2Grow runs on average 3-5 hours per day, at a usage of 8-12 watts/hr - 1.2 kwh per month (I have a power usage monitor on my system and I’m always trying to keep those costs down!)
I would say the expense of this product is the single biggest drawback to implementing it in your systems. If you don’t have a DO meter, those can run $250 for handheld model. The small emitters need to be replaced every year and a half (in my experience) at a cost of $55 each.
Sorry for the length of this post, but I felt like this technology wasn’t getting the proper exposition here, and I think it was one of the best upgrades to my grow system I have made, both in terms of increasing yields and decreasing energy costs.
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Great knowledge to share! Thank you it was a good read
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