They are physically identical to internal hard drives.
As a storage medium, probably have a decent shelf life of 10 years or so, not really sure on these newer drives. The data is so much more dense now. The Mean Time Between Failures of any given drive is only a guide. A drive could fail on the first day, or after 5 years of 24/7 use. Their lab testing is based on some sample of test drives, and not necessarily the same exact models (And they set the criteria to make that number larger)
Best to replace them at any sign of issues for data retention.