Google can prompt you to confirm the login via your phone. It appears to work well: there's a time-out, and this time-out is also triggered if a second login attempt is made in parallel (and reaches the confirmation stage).

So… whichever login attempt gets to confirmation stage last wins (not relevant in this situation), and the confirmation screen on (at least) my phone does not indicate anything regarding location (which is highly relevant).

This looks a little weaker than TOTP (you're basically trading a little security for the convenience of not entering a code while keeping the second factor) and a lot weaker than U2F.