Product Review of the Day: One ‘N Only Keratin Smoothing System. Last week, I used the One ‘N Only Smoothing System on my friend Lindsay’s hair. Her hair is wavy, and VERY thick. She has never had a keratin treatment before and was fed up with how much time it was taking her to blow-dry her hair every day. On Friday, we applied the treatment. After reviewing it all weekend, she contacted me yesterday to report all her good results! Her Favorite thing about this treatment is that it took very little time to complete and has been saving her time each day in styling! All together, she thinks keratin is a keeper!