FreeSync once activated, the flow advances, without increasing latency. This is as good as G-Sync ... at least if the performance level is between 120-144 fps. Below, the Acer screen quickly shows its limits.
A smaller level of performance, such as 60 fps, a very pronounced ghosting phenomenon appears. The ghosting is a natural phenomenon for LCD screens, but various techniques, such as overdrive, so are in principle to eliminate or at least reduce the maximum.
But for XG270HU or disables Acer simply overdrive when the LIF is used (3 options are proposed and make no real difference) or the overdrive was calibrated only for operation at 144 Hz and operating parameters not adapted to the lower refresh rates. But ultimately, the problem is that on this screen and realistic level of performance for most players, FreeSync adds a compromise over for the players: you must choose between flow and no ghosting.
And unfortunately that's not the only problem we encountered. In many games, when we aim +/- 60 fps, it is common to have short passages at 40 fps, or under the lower limit of the LIF range supported by this display. In this case, significant jerks impacting fluidity. It's a little better when the V-Sync is disabled, but it is very troublesome.
We tested several G-Sync screens and no problems of this kind has never been met. Nvidia uses its G-Sync module for applying an overdrive suitable for LIF and avoids rather well the phenomenon of ghosting.