Two things about that:
1. Time: with true U2F I simply touch a pad on my chip (USB A inserted in a laptop), or tap the Yubi on the back of my Android using NFC and I am in. The second factor is virtually instant! Computers and phones never see the keys even if infested!
2. I will never keep my private keys on an online computer. Never. To sign my staked address I have to go to a cold computer because that is where the private keys are stored.
ps - side comments: U2F is going to grow and become the standard for tons of sites anyway. That means that serious security seekers are going to own a secure element U2F chip anyway. Because of how the protocol operates there is no limit for how many sites you can secure using this one U2F element. It would take me pages here to layout how this works but there are links everywhere online. For users its "point and click" easy, and recovery codes in advance make account recovery routine!
pss - bank example: should be the same here when U2F is implemented. When I am logged into my bank and want to change my email or password I am stopped until I do a U2F verification. How nice would that be here? Nobody could mess with someone's account unless they physically held the needed U2F element OR they had the recovery codes. No exceptions!
I agree that normal 2fa would be generally faster and more reliable, but it would still be nice to have that option. You should be able to pic. I have no problem storing my coins on my laptop, so I can sign messages on the fly.