He has certainly shot a lot of Celebrity Portrait's. Does he have any headshot work available to view?
I have friends who are great fashion photographers, but I wouldn't let them shoot my headshots. I would want to see his headshot work first if I were you. Don't go solely on the fact that he has shot celeb's!
A client of mine showed me their old shot which was done by David Hiller and it was pretty decent.
David Muller, I really loved a shot you took that I saw on here that someone posted...Anthony...or Alex or something. He posted mediocre old shots and then shot with you and posted new ones and they were really great. Anyway. They just stood out in my mind. Nice work!