I found out that a lot of the older pfsense appliances including the FW-7535 / Netgate 7535 have an issue with the BIOS that makes the "dd-ed" nano images unbootable.
The instructions to dd then fixup per: _https://doc.pfsense.org/index.php/Embedded_install_on_Netgate_Hamakua
Plug the CF into a working pfSense or FreeBSD system and then run:
boot0cfg -v -B da0
Where da0 is the CF device. Check the boot log to confirm that the device is correct.
Alternatively, use mdconfig( 8 ) to mount a .img file to /dev/md* so it can be modified as above (except using md* rather than da0) before writing to boot media.
After making that modification, place the CF back in the unit and boot as usual._
Are correct for the FW-7535.
Only one more question - will future updates blow up ?
Will 2.2.4->2.2.x have issues?
Will 2.2.x-> 2.3.x have issues?
If anyone knows for the pfsense / netgate appliances that have a BIOS with issues that require manual boot0cfg fixups what the upgrade path is can you let me know here?