Corroded zinc coins/pennies cannot be repaired, and results vary as far as taking them to banks to have them exchanged which used to be the policy of the US mint for damaged coins and currency.
I use the $40 rock tumbler from Harbor Freight, basic cheap aquarium gravel and dish soap from the dollar store. I just use a 50/50 mix of coins and aquarium gravel and a couple squirts of dish soap and fill the bin with water to about 1/2 inch above the coins/gravel and let the tumbler run for a couple/few hours. It will make all but the most dirty coins respectable. There are all kinds of complicated coin-cleaning recipes for the tumbler, but they all pretty much work the same.
You can buy tumbling grit in different sizes if you really want to make your coins look clean and circulated, but I just clean them so that the bank won't kick me out for giving them rolls of grimy, dirty coinage.
The common sense rule though, says any key dates or valuable coins, don't clean other than with a toothbrush, some soap and warm water. Tumbling is a mechanical process that will wear down coins, period.
As for this tumbler, people complain about the belts breaking. They come with 5 belts nowadays, but the reason most people burn through drive belts is probably because they load these things up with too many coins at once. It's called a 3 pound tumbler for a reason.
They also have a 2-tank tumbler for a little more money too if you have tons of coins to clean.
http://www.harborfreight.com/3-lb-rotary-rock-tumbler-67631.html
