so from the video this is only really useful when you can render at multiples the speed of your monitor. Otherwise it'll just get in the way and be worse than either vsync on or off.
ie 60hz monitor, you'd need to be over 120fps render to make this work. So anything from 60-120 is kinda of a no go area. Makes sense as I was trying it on a game with an avg 80fps on a 60hz monitor and it made it pretty jerky.
from what i gather i thought it was another form of triple buffer / back buffer
It means it should still sync to whatever your monitor refresh is but be better than vsync re less input lag ...but will only be smooth as long as one can keep v locked.
A side note re opengl in doom and triple buffering
If i run doom just on the cusp of keeping in v lock and with vsync on i would get drops just under 60fps and would feel see lag now when i put on triple buffer it was smooth sailing .....
so not sure if this fast sync is just a form of triple buffer that's been around for a while now in open gl ...some one with more knowledge may shed some light on this