I've heard that they are pretty basic, and not sufficiently detailed to build an accurate model from. From what I've seen on their website I would agree. It's a shame, since if they were better they would be a bargain. I also understand that they show structures as they are today and not as they were when in use by the Grande.
You can buy good drawings from the Maxwell Collection (see link below) for a lot less as well as other sources... try Coronado Scale Models or Mike Blazak.