I was looking at those a while back as well and I have some reservations.
They say the hydrogen given off is negligible and that is 100% BS or they have no clue how their gizmo works. When you run a current through water it breaks the water down in to oxygen and hydrogen. The amount of each is always the same. For every water molecule you get 2 H's and one O.
It just so happens that that is the exact ratio you need to have a very very explosive reaction that will form water again.
They say its nothing to worry about, but that is BS as well. In my teen years I made lots of bombs by placing a baggie over the opening on a motorcycle battery and collecting the gas while charging it. When you attach a fuse to the baggie and light it, you get one heck of a bang out of a sandwich sized baggie. Ive put them inside a 2'x3' cardboard box and ended up with confetti all over the back yard. Lots of fun, but really dangerous.
In an enclosed rez, you would get a highly explosive mixture in short order and it would be at the perfect ratio for an explosion every time.
I have also read the the emitters dont last as long as claimed and are almost impossible to clean.
More importantly to me - its easy to get 100% DO without having to run those risks or spend that kind of money. They were comparing the emitters to air stones in the video and its well known that air stones are one of the worst ways to increase DO.
I dont know about the O2 in solution and how it would react with the nutes, but I would worry about excess un-disolved O2 as it is highly reactive. I think a lot more testing needs to be done with this tech, but the hydrogen bomb aspect is enough to turn me off