You also need to be aware that in this case, the attacker is/would not targeting any specific device. For brute forcing, all it takes is a dictionary of most common passwords and a list of devices that are exposed. Attackers won't spend too much time on any single device as there are so many options out there.
30 bits of entropy isn't particularly secure against locally cracking a password hashed with sha256 or a similar non password hash. However at 1000 guesses per second it would already take 28 days to brute-force and 1000 guesses per second is pretty fast against any password stored with a properly configured password hash like bcrypt.
I personally auto-generate readable passwords for most websites at ~70 entropy pure brute-force and ~50 entropy if my algorithm and set of inputs would be exposed.
[1] https://en.m.wikipedia.org/wiki/Basic_English