I have extremely frizzy, dry, long hair (sounds attractive, I know) but after using the shampoo and smoothdown serum I have seen a massive difference. The product is expensive in comparison to serums that you can buy at Boots, but for me it's well worth it. I apply some to towl dried hair and then again to the individual sections before straightening. It works wonders. If you have hair that's already in nice condition, you probably don't have to use as much as I do, and so it will last longer, but the serum still lasts me for ages. It's a pitty you can only get it from some hairdressers, I would like it to be available in Boots for ease of purchase. Redken is a product worth buying.