I bought one after the ad popped up on my facebook feed. Tried it for the first time today and it is amazing much better and quicker than straightener and you I didn't have to blow dry my hair first (did it on my straight out of bed dry hair). The knack is to make sure the bristle really go through the hair. Best way to do it is to hold the bottom of the hair section you are doing. It took me about 10 minutes and the back of my hair looked straight (which it never does with irons as I just can't do it properly).
I can already see how I won't be able to live without that little gadget.