Where would you get the bus from? I assume it's meant for connecting passengers, so it would be before you got through transit security?
So, if you wanted to get from departures / airside in T3 to departures / airside in T1, you'd first need to go the "wrong way" through transit security in T3, then get the bus, then go through T1 transit security. And then the reverse to get back to T3. Not something I'd like to try
