Not bad
I got this as a gift for my wife to use in place of her flat iron hair straightener.  She has used it a couple of times so far and says that it works well.  The brush does add volume to the hair as opposed to the volume that is lost when using a flat iron to straighten the hair.  It seems to take a little bit longer than the flat iron and might just not get as hot as the flat iron does.  She has also liked the natural feeling of brushing as opposed to clamping down with the flat iron, but she can get closer to the scalp with the flat iron than she can with the brush.  So it seems that she has started with the brush, but then finished flattening her hair with the flat iron.  My wife also has very thick hair and this might not be a problem for someone with thinner hair.  It does seem to do the job, but I think she just prefers the flat iron instead.  I am hoping that she can get used to it and see if it improves over time.  Maybe it is a technique that needs to be learned?  Either way, she was not too impressed with it, but didn't hate it either.
Rating: 3 stars