Another glass fish tank heater user here, though I've switched to mostly muriatic acid/hydrogen peroxide. My only real complaint is that it's got a "minimum fill" line, so I have to make a giant batch of etchant no matter what size board I do. I often end up not using the tank to do smaller stuff because of this. My tank is also flat (looks like an ant farm box), so it would be even worse if it were larger.
Good luck on it!
Good luck on it!