I just hooked up my Retrotink 2x and, as advertised, it seems to have virtually eliminated lag. I used to get around 8.5 to 9.5 on the auto calibration screen and now I consistently get between 3.5 and 4.5 across several games. I'm not exactly sure what the numbers mean, but I can now play Duck Hunt Vs. and some of the other modes on Barker Bill.
Clay shooting on Duck Hunt and Duck Hunt VS. doesn't seem to be perfect, but I am getting more accurate results from them, as well.
I've noticed an overall less muddy appearance with my retro consoles. I had a lot of trouble with N64 especially through composite on my 1080p flat screen, such as dark levels in Bond being virtually unplayable. But now they are back to nearly as good as on a CRT.
All my retro consoles are running composite through a switcher.