This stuff is great! I had used it several times in the past and was thrilled to find it on AMAZON finally. It works great! If you follow the simple directions: wet surface, rub small amount into stain - it works with very little effort. I've used it on my auto windshields and also on exterior windows of an older house.
Excellent!! had stains so bad on a sink I had given up and thought I would have to replace--this stuff and a little elbow grease made it look sparkling new again!!! Yeah!
It really DOES work! It doesn't smell or scratch surfaces. Not sure what is in it but it only took a part of a packet to clean the hard water stains from the toilet.