I was interested in Google Titan after learning about Yubikeys - https://www.yubico.com/
What do the Titan Key and Yubikey do? I set it up on my e-mail account to where I need my username, password, and I have to plug in the Titan Key to log in to my account. I would feel comfortable giving my friend my username and password to my e-mail, and I could sleep at night knowing they wouldn't be able to log in because they don't have the physical Titan Key.
The key is similar to authentication apps that provide a 6 to 8 digit number to log in to an account, or when you get a text message sent to your phone with a 6 to 8 digit number to log in.
The pack that I got came with a physical USB plug in key and a bluetooth connection key. Both of these keys are linked to my e-mail, so if I misplace one (which I hope to never do), I can use the other to log in.
What is somewhat concerning though is that when I went to the Google Store website tonight to link the Titan Key up above, I couldn't find it on the main page. I had to manually search for it. I hope they're not discontinuing the product already. I actually had to wait about a month and half before receiving it because Google was out of stock. It seems like a good idea of a product, so I'm not sure why it's not displayed on the Google Store website.
I need to add the key to a few more apps/logins to make the cost worth it ($50), but even just knowing my e-mail is secure is a good feeling.