When using it as a uds should be used, I have seen absolutely no need for a diffuser.
That said, mine is currently a twig burner. When cooking chicken, I have a VERY short window to open it without catastrophic temperature spikes. With chicken I run the drum hot (300-350). Essentially all the twigs are kept right below flash point - open it longer than 10-15 seconds and flames are coming out the top of the barrel. As such I have considered using a diffuser (including a butterfly baffle - to limit the uds turning into a burn barrel.
Why do I open it too long? takes a while to load chicken quarters.