This modules enables simultaneously U2F and TOTP (like Gitlab). Users can so use their TOTP instead if they don't have their U2F device.
The difference with enabling both U2F and TOTP is that there is only one page displayed instead of displaying first a choice menu.
In the manager (advanced parameters), you just have to enable it:
This module has no self-registration. You must use U2F and TOTP self registration modules. Example: suppose you want to authorize U2F registration only if a TOTP secret is registered:
$_totp2fSecret
Automatically, U2F registration will be hidden for unregistered TOTP users and displayed then.