IANAC (I am not a chemist).
It technically works, but via the addition of metal ions through basically an anode floating in your pool. So, the resulting pool water is basically like using algaecide all the time instead of an actual sanitizing agent. It creates an inhospitable environment for some bacteria and algae, while still technically going under minimum levels of metals for drinking water.
However, even assuming it technically works at preventing algae (which is still a bit of a stretch), there's a simple litmus test here. If it were possible for a $200 device (that's really just a floating solar panel attached to a copper anode - less than $20 in parts) to actually make water sanitary, then drinking water providers all over the nation would be using this technology, and it would revolutionize drinking water standards around the world. Since it's been around since the 1990s and I don't recall such a revolution having ever happened, I would say it's something close to snake oil.
There's still quite a difference between algae-free water and sanitary water. Algae isn't the only thing to be concerned about. And while copper ions may kill many small organisms, it's not going to get them all, and possibly some of the most dangerous things will get through with nothing in their way.