read-only mode is technically possible, preventing formatting is not as the user has no software on their machine - there's nothing we can do to stop Windows formatting a USB stick without any McAfee software running.
Also, read-only mode would only apply to the EERM container itself, not to the actual USB stick (again, no software running) so it would not be possible to protect the stick itself from infection, only the files in the secure container.
So, not too useful I think.
For me it is very useful, because an encryption software like McAfee EERM should have an autoprotection option to prevent users to deIete the EERM.
As I say, before you run eerm there's no mcafee software running, so we can't do anything at all.