I'm finding M.2 PCIe SSD cards for Mac Pro 5,1 to be very confusing. I'm looking for cheap, not super-fast. I'd like to boot from SSD. This is what I think I know: AHCI M.2 - M-type key - works fine in Mac Pro tower without drivers using any 3rd party M.2 to PCIe card. Bootable. Older tech, rather expensive and harder to find. NVMe M.2 - M-type key - will work but have to install special kernel module. Can't boot. Likely to break with OS upgrade. But relatively cheap and abundant. (Q: Why does 'about this Mac' show NVMExpress under Hardware if you need to install a hacked kernel module?) SATA M.2 - B+M key - Q: Is there any way to make this work in a Mac Pro? Using just the PCIe slot, or do I need a cable? These B+M key units seem to be cheap as surplus and leftovers from upgrades. I could imagine booting from an old 128GB SSD in the drive bays, and having another NVMe SSD for user data, but the fact that OS upgrades will be messed up bothers me.