Do not even consider mounting this through wallboard. When you lower and extend the display, real pressure is put on the screws. Leverage!
Here is a template for the back mounting plate from their web site. (The whole site is very informative).
Note that the arm supporting the TV is fixed on to the back mount. This means that you cannot move your TV left or right on the back mount. If, like me, you want your display mounted exactly in the center above your fireplace, your weird studs may
prevent you mounting the back mount to achieve a centered display. However, you can slide the display left and right where the supports holding the display rest on the front of the arm. I found that if you slide more than two or three inches from center, the whole thing does not work quite as well.
I suggest you make a template out of cardboard to see if the mounting hits your studs and results in a centered display. Also if you are hiding the wiring in the wall it will enable you put any cable / power boxes in the open areas of the mounting plate. If you print the PDF full size you can make a full size cardboard version.
If you are fussy, this requires a lot of pre planning.
I have fat cables which are hidden in the arm - and I haven't bothered to hide them as much as I could.
Send me a private email and I can send pictures if you have any issues.