I'd get the Pro version. You're 5DIII is likely under warranty, you're buying a 1D X. The multipoint test can reveal issues with the camera's AF system. Even if your lenses are fine, different lenses have peak sharpness at different apertures - that info may (or may not) help. I figure if you're spending thousands on gear, a few bucks on software to get the most from that gear is money well spent.
Good advice and I would like to stress the value of the Aperture Sharpness test. It's good to understand your lenses strengths and weaknesses so you know what to avoid and what to exploit. For example, I was a little surprised to see the results of my 24-105L. 24mm: good at f4, best at f/5, then tapered off from there. 105mm: horrible at f4, best at f/8, then tapered off from there. Good to know! So I'm opening up a bit more wide and stopping down a bit more zoomed and the images are looking great, better, and I know exactly why.
I also use this feedback for the AFMA testing as well. I test aperture sharpness first, then AFMA test at the sharpest aperture. It stands to reason that I should get the most accurate results at the sharpest apertures, plus those are the apertures I'll be trying to shoot around anyways. Is anyone else aware of a flaw in this logic or testing methodology? (edit: this is not exactly best practice, read through this thread for more info)
One last thing, at the time of this writing I can't recommend the software for Mac. I had nothing but problems with it and it made for one very frustrating evening. I now run it on a windows 7 VM without issue. Just aheads up!