I have clip-in extensions and use this brush to tease the sections before I clip in my wefts.
It works well and is much more gentle on my scalp and hair than a rat tail comb, but the bristles tend to fall out. When I first got the brush I touched the bristles and TO MY HORROR and bunch fell out. I was about to return it but saw that if I was careful, the bristles didn't fall out much.
I think this brush is fine, but if you had light hair the falling black bristles would be an issue.