I know this is a dormant thread, but I thought I might respond anyway, in case someone else is looking at FoCal now. I bought it a couple of weeks ago for use with my 6D. I wasn't sure it would work as advertised, but it promised so much that I decided to bite the bullet and try it.
Bottom line: It works great, and gives you some information that would be difficult or tedious to come by otherwise. The 6D is capable of full automatic operation with FoCal, but even it weren't, or for those with other cameras that only work in semi-auto mode, I'd still recommend it.
I'm not very good at, or very interested in, a lot of pixel peeping testing. Once you get the hang of the required FoCal setup (target distance vs. focal length, some simple lighting concerns), you tether the camera to your computer, make a few mouse clicks, and walk away. The s/w does everything else for you, and it does it pretty quickly.
I'd never given focus miscalibration much thought before this experiment. I was really surprised how much difference it made with my 16 year old Sigma macro lens. I took a series of test shots before the procedure using both uncalibrated autofocus, manual focus, and manual focus with Live View. Surprisingly, the sharpest shots came from the autofocus-after-calibration set. Obviously, that lens suffered from a misfocus bias before calibration. But I'm not sure why the LV manual focus shots weren't better still, as I would have expected, but they weren't detectably better, and that says a lot about the usefulness of FoCal, as the uncalibrated set were obviously not as well focused.
Interestingly, my 24-105 L required not focus adjustment at all, at either end of the focal range. My 50 f/1.4 needed a small adjustment, but also turns out to not be as consistent in its focus as the 24-105. FoCal also demonstrated pretty clearly that the 50 1.4 suffers from focus shift when stopping down, which I figured out on my own years ago. I guess you get what you pay for. I tried a cheap, ancient Tokina 19-35, and that turned out to be pretty consistent, and was substantially sharper after corrections were calculated for both ends of its range. My 40mm STM needed practically no correction, did not autofocus as consistently as some of the others, but tested remarkably sharp nonetheless.
In addition to calibrating focus for each lens, I also like the plots it can make of sharpest aperture, focus precision, and sensor dust. overall, I think FoCal is a better investment than one of those inclined ruler type of focus target setups.