It just needs 16-24 volts.
A chime or no chime should have no effect on the operation.
There is even an option in the app to have it not ring the chime.
You have to create an account which is why it's easier to just use clients phone. Or use yours and whatever credentials they want to set up the account then they can just login from their phone.
Doorbell rings in the app for whoever is logged in with the app. I haven't got up to 5 but 3 works. I haven't tried 2 people anwersing and talking at the same time though.