I've tried both continental and Eastern FH grips on flat serves. I can get a little more wrist snap easily with continental, but I've always found it's a lot more consistent for me, and almost equal pace with the Eastern FH. I don't know if it'll hurt me in the long run, I'll ask around.
Using an Eastern BH grip also greatly increases my consistency, it was how my hand naturally gripped the racket the first time I served. I think my first serves all had topspin, although not very much kick.
From looking around on the forum, a lot of people and most pros all use a continental grip. So I've been trying to get it better, and use it for first serves. I usually use a consistent flat second serve with an Eastern FH grip, or sometimes topspin.