I find the lines on the mat and the lines on the ruler too confusing for my brain so I always use the back.
The thing you need to remember when cutting with a ruler and no lines is that the amount you want to measure and cut is under the mat. It feels odd at first and may be what the video explains. If you want a 2 1/2 inch strip, 2 1/2 inches is under the mat with the edge lined up with that line.