I've been using this for like three weeks now and the difference was huge for me and I don't think I'll go back to regular non-capped/non-vsynced fps. I don't know if it's because I have a pretty old monitor though, XL2411T from 2014, but the image is so much clearer with than without, it's night and day.
I've not really noticed any input lag at all, maybe just old people things, and even if it's there, the picture clarity is worth it for me over the tiny amount of possible reaction time I'm missing.
I'd suggest that any one tempted to try this, go for it, it doesn't take long at all to set up and it can be super worth if you like it.