The Pool Frog is one of a class of devices that put copper (and sometimes silver) into pool water.

Copper:
+ kills algae
+ inhibits some bacterial growth
BUT ALSO
- does NOT inactivate viruses
- does NOT kill bacteria quickly enough to protect people
- does stain pool walls
- does turn hair green
- is NOT 'natural' -- it's in the toxic 'heavy metal' class, if you want to play chemical name games.
- is NOT 'chemical free' -- copper ions are just as 'chemical' as hypochorite (chlorine) ions.

Basically, we discourage their use because they don't do what they are supposed to, very well, and they do quite a few things they are NOT supposed to do.