USB or microsd are great for something like a non permissive environment because they are more hideable. At least for now most people have time corruption as a greater risk than typical NPE problems. All flash based memory has tiny batteries which are necessary to keep the data from corrupting or ceasing to exist over time. Leave them unpowered too long and your data will poof away.
A simple mitigation is multiple copies, hashes, and a schedule of regular testing file reading and hash checks on ALL devices copying to new ones if any corruption is spotted on any device.
