It's possible to do, but i'm not sure if this exact one is legit.
In order to completely and perfectly separate the O from the H, there has to be a membrane in between the two cathodes. I'm not sure right now what that membrane is called, but it's probably something like a Proton Exchange Membrane. Actually, I'm pretty sure that is what it's called.
Anyway, I think a PEM works by allowing ONLY the proton through it's membrane.. basically, to set up a cell like this, you have two cathodes (two plates, one positive, the other negative). In between these two plate/cathodes, you have the PEM (Proton Exchange Membrane). I'm thinking this allows only the proton through because the electron is bigger than the proton, and doesn't fit through the membrane (NOW THAT'S MICROSCOPIC!!!) So, since the proton can't fit through the membrane, it must stick to one side. If the proton is only on one side, then each gas is made on either side of the membrane... etc
I may not have all the details right, and i'm probably not going nearly into enough detail to explain it accurately.
I would say, that unless this cell had a PEM inside (which would cost around 200-300 dollars for the PEM alone) then it's not perfectly separating the HH from the O.
It might be doing it slightly, and if it is at all, I doubt the cell is very efficient.
The only way that i can think of how to cheaply separate the gasses, is to have the two plates with a plastic-like plate in between. The plastic plate would divide the metal ones, but allowing a space in the bottom, so that current can flow through. I would think that this wastes A LOT of power and wouldn't work perfectly either.
(THAT IS JUST MY 2 CENTS, SINCE NO ONE ELSE REPLIED TO YOUR MESSAGE YET