The website itself is poorly organized and confusing. They will send you a plastic card the size of a credit card as a two-factor authentication method. Making changes is a hassle. I had to mail a form to add a bank account.
Doesn't really seem worth it. Only seems practical if you are really rich and need a place to stash money above the FDIC limit.

Has anybody used Treasury Direct website for treasury bill purchases ? Feedback...
Thanks!