I've only taken the standard GTD seminar. I haven't done Roadmap, Mastering Workflow or telecoaching. But a friend of mine, who has read the book, attended the regular seminar, and listed in Getting Things Done...Fast! seminar recording many times did about three telecoaching sessions with Meg, and swears by it. He initially had reservations due to the cost of telecoaching, but now feels that the format is so much more tailored to your personal needs, it was easily worth it.
Though he never took the Roadmap or Mastering Workflow seminars, it was his understanding that the only difference between the two is in the presenters. Roadmap seminars are given by The David, and MW seminars a presented by other staff.