It's not a substitute for having a strong password. The feature does a good job of disabling USB at a software and hardware level but nothing is bulletproof. USB is also not the only usable vector.
What you can do is have a diceware passphrase as your primary unlock method, and a fingerprint + PIN combo as your secondary method. That way, you only have to enter your long passphrase after a reboot or every couple of days when it asks for it, and use fingerprint + PIN which takes no effort for daily use.
To avoid being prompted for your passphrase when you're out and about, make a habit of unlocking your phone with it daily to reset the timer.
Soon, we'll be providing a way to generate random PINs and diceware passphrases to make choosing a secure unlock method easier to do.
