@LindsayC Just an update on what I've ended up doing. As we wanted to use the ethernet connection as our main comms, we've implemented the DuetHTTPclient and telnet connection together.
The DuetHTTPclient has the full object model updating in the background that can be queried regularly with less time-critical stuff like reporting in the UI things like temperatures of chambers etc.
The telnet allows more time-critical comms without the overhead of the DuetHTTPClient like needing to wait for update of the object model.
Single cable solution with a lot of flexibility.