I stumbled upon this thread. It learns me that the ISA CF adapter will not work with the Sidecar because of conflicts in the BIOS. This can be solved, but I don't have the skills nor knowledge to perform this.
So this is the outcome at this time of the ISA CF adapter adventure.
I tried the Western Digital Filecard and it worked a few times. After that the Amiga partition vanished. So it's not reliable anymore.