Compared to my old Focusrite Scarlet, I get less than half of the latency at the same buffer sizes, meaning I can use larger buffer sizes than with Focusrite for better VST performance while keeping latency low enough. RME's custom USB driver provides near-thunderbold performance over USB 2, which is impressive.
The UFX II has gotten ALL features of the UFX III added via driver and firmware updates during the last year. Even their decade-old discontinued interfaces continue to get all improvements that their hardware can physically handle. This level of long-term dedication to supporting and improving old hardware is why I won't use non-RME interfaces going forward. Other brands tend to have the attitude that their hardware's feature sets should be locked to what it was at release day and never backport any features, just bugfixes.
The UFX II has also gotten "secret" hardware revisions since its release, adding SteadyClock FS and improved components so if you buy a new (revision 7) UFX II today you pretty much get a UFX III without MADI support.