This is my first cold storage wallet. I have recently read that I shouldn't have the bulk of my cryptocurrency on exchanges like Binance, Gemini, Coinbase, etc., because it's not very secure (for a variety of reasons).
So I heard that the Kubikey and the Trezor were very well liked by people smarter than I am.
I got the Trezor because the article I read said that "it doubles as a cold storage wallet."
So far, I'm pretty sure that's all this is--a cold storage wallet. It's not a U2F device, as far as I can tell. I don't think I can use this in lieu of my phone number as a U2F (using your phone # for 2FA is not very secure--not many people know that, I just read about it only recently).
UPDATE: This does function as a U2F! It integrates with gmail (and I'm sure other sites) easily. U2F is like 2FA (2FA is when, for example, you put in your password (1FA), then the website sends a text message to your phone with a verification #. You put in that number as well, just so someone can't log in with just your password; problem with 2FA is that hackers have workarounds for 2FA, so they don't even need your phone.
U2F solves all the security vulnerabilities that 1FA (password alone) and 2FA (password + verification code) carry with them. The only way to log into the website is to enter your password, AND ALSO have this special device and press the checkmark on it.
This means that, even when the hacker knows your password (they probably do) and can gain access to a verification code sent to your phone (they might), they can't gain admittance to your website account unless they also have this device plugged into their computer (and know your secret PIN code for the device as well).
In short, this is a hacker's worst nightmare.
Before this arrived, I was worried that the USB cord was too short, which would mean it would be awkward every time I wanted to access my wallet. However, it is long enough for me to remain seated in my normal spot and comfortable use the Trezor.
Other reviewers mentioned the keys being small, but I didn't encounter any problem at all (I have thin fingers though).
One or two reviewers said something about the firmware tripping up when they tried to install, and one reviewer said you have to plug it directly into a USB port on the rear of your laptop (I don't know what he's talking about).
I have a 4 port USB thing that plugs into one USB port on my laptop. I just plugged it into one of the 4 ports, and everything worked fine.