PLAN-B,
Yes, this jig is adaptable to any size joint by changing the flippers and/or scaling the size of the entire jig. The size of the jig shown in the video would not be ideal for making 6 inch jewelry boxes with 1/4" joints because you could not conveniently clamp them inside the sliding box.
The flippers are mounted on a 5/16" steel rod held in place on a steel bracket with a cap nut and a very small cotter pin. You can make a set of flippers to complement the width of the dado joint that you want to use. You just need to follow the three rules that I wrote in the post above.
Carl