I made my test with a HD Camera connected in HDMI to a Blackmagic Studio, setting are 1920x1080, 25fps, best quality, the background is a Prores 1920x1080 25fps movie. The subject ( myself ;-) ) was on an very approximative green screen ( in terms of light and regularity). In that very basic conditions, the result was surprisingly good... So I am impatient to test in better conditions.
But it is still less impressive than what Resolume 4 is able to do with the same sources : much better soften edge, acurate color setting, little less latency...
It seems this FFGL has been writen almost 5 years ago. May be there is today some way to "refresh" the code? If only the feather function was efficient... No little genius around to have a look inside the code? :-)