OrangeKnickers, they definitely do work. I don't think they damage hair, I use mine every week! (I'm not dirty, just not supposed to wash afro hair too often).
There's a YouTube video of a girl reviewing/demonstrating the Lee Stafford one here (although at the end it doesn't look that different so not sure if this is as good as Batiste). She says don't do it too often but personally my hair hasn't suffered: Lee Stafford YouTube review
The Batiste one is like a spray-on powder, and definitely well thought of (when I started my reviews site I was surprised it's actually the second-most reviewed product after GHDs!): Batiste reviews
Also Boots Expert does one which doesn't come out like a powder spray, but still works.