I used the mild strength and i'm a 4a. i left mine on for 20-25 mins and it took very well.
My lil sis applied mine and she was very thorough with her application, she made sure to smooth and properly coat every area she needed to. I haven;t had any of my (unfortunately characteristic) hair troubles for the past 4 weeks!
My "affirmed" hair actually looks a lot shinier and healthier. Then again, what works dfor one person may niot work for the next, how long are you leaving yours on???