Agreed. The reason the SilverTron doesn't have the polarity switching is that the designer knows what he's doing when it comes to making silver. Using electrolyte (non-toxic sodium carbonate and distilled water stops the silver plating to the cathode. So on the basis that you're "making your silver the right way" you would never need to have polarity switching.
ans in answer to your question on cleaning a bullion.........Hold it in some pliers and hold over a gas stove burner until the bullion burns off back to white. Heat it enough until the flames coming off have a slight red glow. This turns the silver oxide back and means you're not wasting the silver by rubbing it way! let it cool and you're good to go. No scrubbing necessary. Search SilverTron forum. If you're into this stuff, you'll be glad you did. They had the best BS detectors i've ever seen. You'll be making perfect Colloidal Silver every time! and if it's not, they'll tell you why!