dna kits question

I usually post on the adult adoptee boards, but haven't had a response...I was wondering if anyone has used an at home dna kit and what were your thoughts. My bmom wants to do one with her "maybe" 1/2 brother. She would like to see if the man she grew up to think as her adoptive father was really her bdad. We want to order a kit, but don't want to waste the money if it isn't worth the results.Any comments would be great!!