I have a shoot coming up where I'll have the talent in front of a green screen and he will have to see himself against the BG that will actually appear on the video, so he can interact with stuff on the BG.
When I lecture on greenscreen production that's the program I use.
On the "Input" button there is a "Live Input" (or something like that) selection.
It's extremely easy to do.
I have used Ultra2 on my last 2 productions with excellent results.
The last one was for a musical instrument distributor and i had my talent be all 4 members of a Rock Band, simultaneously, playing at Stone Henge. It looks great and was a helluva lotta fun to do.
It was all shot on a 12' x 24' portable green screen.