I have had them in the past. When I did it, my hair was super straight for about a month then gradually started to revert. Not just at the roots. The coating on the hair starts to come off and it just gradually goes curly again. I stopped doing it because it was a lot of money and a tricky process. You had to avoid washing your hair or exercising or getting it wet for about 3 days after it was done, preferably more. This was to allow time for the coating to bond. Also, during that bonding time, it was better to avoid tying it up or wearing a hat (it can change the shape of the hair while it's still setting). And then you have to wash only with special shampoos. But that may have all changed (it's been a few years since I did it).
