I have been using lightboost for a while now and i would say give it a try, after using it for so long switching back to 144hz even felt a little blurry to me. I heard about the input lag but really i can't notice any at all, only the colors are a bit darker so i up gamma slightly and raise saturation on my gpu. it's all personal preference i guess but worth trying imo.

the benefits are imperceptible unless you have extremely consistent fps. and even with current implementations of lightboost on newer monitors, the input lag is too disadvantageous to warrant its usage in competitive play.

i reached this conclusion after extensively testing lightboost + benq's dyac with different strobe rates & custom resolutions.

g-sync, on the other hand, is much more useful in practice because of poor fps on most platforms when playing newer games

#1
Yes, just try it, takes literally 2 minutes to set it up and 1 minute of that is rebooting. Need to recalibrate colours a bit because it makes the VG248QE suck even more, but it's doable to get to at least the same level or better than it is uncalibrated without LB.
Screen tearing is unrelated to LB. Fps != refresh rate you get screen tearing.
The input lag is a technicality. While the frame changes (top to bottom) the backlight is turned of so you can't see the half finished frame. So technically you do see the new position of your crosshair 1-2 ms earlier without LB, but do you really believe that the information you get while there's a new frame above the crosshair and the old frame below the crosshair is all that critical and will be instantly recognized by your brain while the scanline is still moving?

#3
How did you measure the input lag?

I use strobelight to enable LightBoost, which is extremely easy, although there are other methods. I turn it on right before I play and simply go back to 144 hertz when I'm done and want to do things like enjoy videos brightly.