I know about the VIP tours that Disney offers and there is no comparison, if you ask me.
I wouldn't do a VIP tour that wasn't run by the actual theme park (Universal, Disney, Seaworld, etc.) for several reasons.
Case in point: Michaels VIP tour service is on the web (Google it). This guy used to be a Disney VIP tour guide. He quit and set-up his own business and a very successful one at that. In observing his site, he portrays a great service with many people writing on how great it was.
While Michael's and the other tour services that are out there try their best, they are "in the dark" so to speak. Private tour services cannot access backstage areas for quicker entry into the parks, they are at the mercy of what is available for dining reservations and the Fast pass system that all guests can use is what they are limited to when trying to expedite a guests visit.
Hope this helps. If you try it out, I would love to know how it goes.