Th is product is amazing...at least for stainless mugs!
This product ABSOLUTELY works on stainless steel travel mugs.  I was skeptical, but it total ly worked in 5 minutes.  I used boiling water and an ounce of cleaner per cup of water.  I had a 16 oz stainless travel mug that I use for coffee, and other than soap and water I had not cleaned it since I bought it 15 months ago.  It was highly stained.  In 5 minutes it was clean.  I had to use a bistle brush and then a dobie pad to get what had been loosened up on the bottom.  It only required light scrubbing for a minute to scrub off what had been loosened up.
Rating: 5 stars