The gas block journal is the area of the barrel where the gas block sits. On the MP10 it is shorter than standard so you'll need to use what is called a "micro" gas block, they are only about an inch long and will sit on the small area where our larger low profile gas block will hang off the front and not be fully supported.
As far as KeyMod it's just a different method of attaching accessories. The original 308 SS hand guards uses small threaded holes to screw rails and panels to the hand guard, but you are limited to what we make since it's our proprietary design. The KeyMod is basically a universal attachment system, anyone's KeyMod accessories will fit on our KeyMod hand guards. Because of this KeyMod gives you a lot more options for aftermarket accessories.
Do some reading up on KeyMod and M-Lok and see if there is one you prefer over the other, or if our SS hand guard will work for what you want to do.
Thank You
Andy
MI