Hi Ian,
In our case, it happened was that we were on the market for a ISV solution for BI at a time when Jet Reports inc. had not yet released the Enterprise product. At the time they did, we had already committed to training in using and setting up Bi4Dynamics.
Since our team was already familiar with Jet Reports, we resort to either product depending of the context: Jet Reports Essentials for direct reporting from the NAV database; Bi4Dynamics when using a datawarehouse.
Nuno