Has anybody tried this for Premiere, and if what do you think compared to the build in keyers?
Since there seems to be a free trial, it would be easy enough to compare Robuskey with Ultra (part of Premiere Pro) or Keylight (part of After Effects).
I found that with a reasonably well shot green screen, both of those are OK.
If someone were to shoot some mediocre green screen footage and share it, I suppose we could all play with all three and see which is the best. But even then, unless you do a lot of keying, the price tag on that product seems a bit high compared to the other two - which are free with the software you already own.
There is some decent (but not perfect) green screen material available for download. Along with motion tracking shots. Check it out on a sample page I made while explaining how to put flash on a web page.