Used Tarnex a long time ago. Never again.
Coin tumblers are great for really grimed coins, but make sure before dumping ANY coin in the tumbler that it isn't worth anything first. Tumbling is abrasive, and will degrade your coin.
For good coins, use olive oil and let the coins soak for at least a week.
Next get a pint of acetone. Using a clean cloth-covered flat surface, preferably outdoors, open the container and dip the end of a fluffy Q-tip into the acetone. Quickly wipe the coin in a circular motion, including the rims. Acetone is the ONLY cleaner that should be used on higher-end silver or copper coins.
Even so, coin may not pass through the modern coin grading experts unscathed. Case in point: received a bonus prize from an Ebay purchase of an older Dansco wheat cent album. By close examination, found the 1909S cent to actually be a 1909 S VDB cent. Coin had been held in the album for at least 50 years by scotch tape, which had solidified on the coins and made them barely recognizable. Took them to a professional, who advised the above method, after performing this operation on the 1909 S VDB mentioned above. Submitted to PCGS afterwards. Coin was returned slabbed, no grade, identified as "authentic, altered surface". If Scotch tape left on a coin for 50 years will result in an "altered surface" designation, try to imagine what a tumbled coin would yield.
BTW, sold that slabbed 1909 S VDB cent for $705 on Ebay, which was sent as a gift for buying an incomplete Liberty nickel set, which had the same problem: held in the folder by tape. Was able to clean all of the affected coins. But that 1909 S VDB was a treasure all to itself, don't you think?
