My friend had some extra crest whitestrips leftover (about 2 weeks worth) and gave them to me to try out since my teeth were looking like they were premanently stained with mustard. They were sort of difficult to apply, and the first thing I noticed was the subtle yet distinctly bad taste that filled my mouth. It wasn't so bad that I immediately took the whitestrips off, but for the hour and a half I had to wear them a day ( 3 times for 30mins/day) I couldn't stop thinking about when I could take them off. When I finally did take them off I rinsed my mouth out multiple times but was still left with a slight aftertaste. I stuck with it for two weeks however, and the results were noticeable. No longer did my teeth look like they were permanetly mustard stained, they were actually almost white! So while I wouldn't recommend these to a friend, I would like for a similar product that didn't have the same taste as Crest Whitestrips.