That trailgrader is impressive. The part 1 video shows some real rough road to grade and I can only wonder how long it will hold up with the imbedded rocks. Seems it would be super for a drive of gravel.
The weight will be important, supplied well with the water barrel. The length between the rear wheels and the tongue connection is also good for a level road bed.
Along with digging the old gravel up, then smoothing it out and not forgetting to pack it down before the gravel loses its moisture, this grader idea is a great one to have a good drive.