Jet Express is basic and free tool for analyzing NAV data through Excel. You use online NAV tables and you have easy possibility for report creation.
Jet Essentials is not free tool. It provides advanced tool in Excel analytic (e.g. Schedule reports), but you still use online NAV tables.
This is a good idea for easier reports with not so big tables. If you have big tables or if you want complex reports, you need OLAP cubes. If you want this level, you need to use Jet Enterprise.
I suggest to see other BI tools, as well. I prefer BI4Dynamics. This is full OLAP tool with a lot of predefined reports and price is not so big. YOu can download trial version and try it by yourself: http://www.bi4dynamics.com/
Of course, you can find another BI tool for NAV.