[mike-cardwell]

This is supposed to secure you on an untrusted computer. It doesn't. There are loads of attacks still. The moment you log in, the attacker has access to your account because they control the browser you're using.

What it protects against is basic key logging attacks (software and hardware). These are the most likely attack you can expect to see, so protecting against them has real life value.

The safest thing you can do is never use an untrusted machine to access important accounts.