Well, I've got good news, so/so news, and bad news.
Good: The patched GBA Backup Tool 0.21 works great. Though I had to figure out how to apply the IPS patch, hadn't done that before. (Hint: Lunar IPS)
So/so: FAS1 works with my Flash2Advance 256M Flash Card, PCB ID: (H)94V0 1203...