Why not sign up genius?
Sign-up genius doesn't allow me the freedom to rearrange the schedule or set people in positions they are experienced in and it consistently had problems sending out group emails for me. What I am going to do is spend this season building a sort of e-mail rolodex of all the people who are trained officials that can work for CCDG bouts and start group e-mailing myself and using officiating groups on facebook to get a wider swath of trained people interested.
When I did use it, I always told people that I had the right to move them where needed on bout day. That and I would let the people I knew had experience in places I wanted to be know first so they could sign up there.
However all of this winds up moot when you have more NSO connections than I did.