Got my hands on a Dell Latitude ON module. Turns out it’s nothing more than a 2 GB flash module that fits in a mPCIe slot and is wired to the USB lanes. Shows up as /dev/sdb.
I do have a couple of old laptops that don’t have a secondary SATA drive slot, but do have open mPCIe slots with USB lanes (no mSATA lanes). The Latitude ON module would allow for a dual drive system, albeit a rather crappy one. What would you put on a secondary internal drive if it were limited to 2 GB and USB protocol?
Total tangent, but IMO this is the state of the art in data retention: https://superuser.com/questions/374609/what-medium-should-be-used-for-long-term-high-volume-data-storage-archival/873260#873260