McGuffey Coffee Residue Cleaning Tablets Coffee Grease Cleaner Easy Removes Stubborn Stains Cleaning Tabs for a Coffee Machine, Sports Water Bottles, Tumbler & Mug (16 pcs)

Q: Is this product safe?

I'm not sure what you are referring to as "safe" . In what context?. It does clean residue very well. I used it in my coffee cups and metal thermoses. It is not for consumption, nor did I stick my fingers in it when it was working. Hope that helps.

Q: Is this product good to use?

Yes works good. Need to use hot water(not boiling) since the hot water activates it to work.

Q: How long can this product be used?

If you have a heavy buildup of residue, let it soak one hour before rinsing. But I prefer letting it soak 15 to 30 minutes and then lightly scrub with a soft bristle brush. It’s not complicated so don’t make it. The stuff works.

Q: does this work with stainless steel cups?

Yes, it does. That's actually why I ordered it in the first place. My stainless thermoses were horribly covered in brown stains that would not come off. Now they are sparkling clean!!