Denitrators like this are a fairly standard hich tech product - deltec, aquamedic, STM and any number of other equipment manufacturers sell them. They use either a standard bioball I think , though I've seen some using sulphur balls that are consumed. I think if you use bioballs you need to feed 'them'.
They really on a really slow rate (drips per minute!) to work, and I think they can crash quite horribly if you have a powercut. I hear that until they're tuned they're difficult to maintain, but if you're going to have a large, predator marinetank they're handy - if you hav a spare $10000 dollars to spare (yes thats right) Deltec sell a very nice complete tank set that includes all these.
I would guess that for many people the appeal of a Jaubert plenum or DeepSandBed setup is greater, but they still sell a bunch of these things, and they do work. You still need to do water changes as there's more to (marine) life than the nitrogen cycle.
As a final note on bacteria, if you look in Fossa and Nilsson they have bacteria counts for a reef floor sand bed, and in the aerobic part of the floor, there are almost as many bacteria of the type described as 'anaerobic' as there are 'aerobic'. That suggests that the possibility for anaerobic nitrate reduction is always there, but doesn't happen as it's going to be chemically difficult for a weak reductive chemical transfer to happen in oxidative conditions
