What is the reason for the stiffener in the tutorials? Fusing it so that the bottom won't fray? Or is there some other advantage to having the reinforcement in them?

The way I make the flashes is that I have ribbon, fold it in half and then sew it across the top for the elastic to go through. Then for the bottom I cut the triangle and sew the two sides together which would keep them from fraying further.

I think with my method, the ribbon is super cheap and all I really need is thread. It's easy too but they still look nice. Also, we can use the same elastic for all the different ones because I sew the flashes so that they can slide off and on easily.