I picked up a Babyliss one from Boots as a Black Friday deal. It is fabulous! I have fairly fine, straightish hair, but it is annoyingly frizzy at the back where it's going grey.
I'd wanted to try one for ages but didn't want to pay Dafni prices, nor did I fancy a cheapo Chinese number which might set fire to my hair.
I find it way easier and much, much quicker than straighteners (and no burns!). As others have said, it doesn't give you that poker-straight, glossy look you get from straighteners, but I'm just after smooth, straight, frizz free hair. I like the fact that you can use it to turn the hair under at the ends. The effects last until the next wash.