I would strongly recommend against selecting a different login shell via /etc/passwd, doing so will blow up with the next sysupgrade (conffiles are kept, including /etc/passwd, while user-installed binaries (/bin/bash) that are not part of the default image are dropped - leaving you without a valid login shell for root --> inaccessible/ semi-bricked device).
If you like bash and assuming your device has enough flash/ RAM/ CPU cycles left, there's no real reason not to use it, by calling it manually - but configuring a non-default login shell is a bad idea.