The FMD and the Insight are essentially the same hardware, but that is where the similarities end.  They use different plugs and cables.  They run different firmware.  The FMD can calibrate a NAV2, the Insight can't.  You can not load the Insight firmware on a FMD and you cannot load the FMD firmware on the Insight.  You can not do yield mapping with the FMD.

I am running a FMD in a MT765.  The steering interface in the FMD is very good.  The FMD has some what limited product control capabilities and must have the Ez-boom or a 3rd party controller to do product control.  It must have the Ez-boom to do section control.  It does not support planter section control, but I think it will drive the Rawson.  Data logging in the FMD is a joke (Sorry Art).  You can get a polygon shape file coverage map that has rates in it if the FMD is connected to a controller.  But it will not log varieties or product changes and very little software will support the polygon shape files beyond printing a map.

The Insight has far more control and logging capabilites than the FMD does.  The Insight supports planter section control now and it will do multiproduct control.  The FMD does not.  But the Insight will not calibrate the NAV2 directly.  It requires a laptop to do calibrations.

You will be pushing the limits on Omnistar HP to get 2-4" repeatability.  You might be satisfied, but you will have to try it to see.  You may end up needing RTK to get that kind of accuracy.  If you have a local RTK network, that would be your best bet.