I have the I-magic, I think the difference is in the motor brake, the fortus will allow you to free wheel and appear to accelerate, ie when going down hill.
Personally I wasn't bothered about that and used the saved money to buy several of the Tacx DVD's, well worth it in my mind as you then are actaully riding a course, resistance increases and decreases along with the profile of the course, including hurting like hell in the Alps.
Yes turbo's can be boring, on a regular one even with music or tv I can only manage an hour, with the i-magic and their dvd's I have no problems doing 3+ hours.