D.W.
I have had natural (African American) hair for 10 years now. I've never used or know of anyone who used KeraStraight. I would think that if you wanted to simply control the frizz of their beautiful curls, that KeraStraight wouldn't be the product to use. I use almost all of the John Frieda, Frizz-Ease products to work WITH my curls/hair texture. I use the Smooth start shampoo and conditioner (I only wash my hair a couple of days a week, but I wet and comb through the conditioner everyday). While my hair is damp, I work the Frizz Ease hair serum to control the frizz. Then let my hair air dry. the serum lets the natural curl pattern show, it just keeps it from poofing up. On days I wear my hair straight, I shampoo/condition, but I use the John Frieda 3 Day straight spray, blow dry on cool using a round brush, section and flat iron into my style. I wrap my hair at night with a silk scarf (you could use a silk pillow case too) which keep it smooth over night.
Edit: I get the products at Target, Walmart, Ulta, Walgreens.