The body saw is an excellent progression from standard planking. Outside of just holding a plank longer, most people don’t progress that movement to get functionally better. Body saws are a great step up from the planks. The varying length of the level makes this exercise much more of a strength exercise, rather than just a stability exercise.
Start on your elbows first, as in the video, and another progression from there once the elbows get easy, is to go to a pushup position to the perform the body saws.