Interesting to learn about other related tools. I built a similar variant called ctenv (https://github.com/osks/ctenv). Focused more general containers and not specific to agents, but I'm using it for that via its configurability.
One thing I wanted was to use any image in the container, which shai also seem to support in the same way (mounting a custom entrypoint script). And same reason for not using devcontainers - make it easy to start a new container.
There are banks/companies that require BankID, but there are several big banks that have alternative methods. It seems that only Swedbank of the big four require mobile BankID for sign in.
One thing I wanted was to use any image in the container, which shai also seem to support in the same way (mounting a custom entrypoint script). And same reason for not using devcontainers - make it easy to start a new container.