That is a great youtube tutorial.
For mine I use 8 # Density Mineral Wool. When I read all the stuff, I thought understood the numbers that higher density meant better absorption.
Anyway regardless they do work very well and the price was very nice. Way cheaper and easier to get than the 703 or 705. I got them locally at a great deal. You have to call an insulation supplier. They seem like they only sell to contractors, but they sell to anyone with cash.
For the frame, I used aluminum drywall beading. A few cuts and bends with sheers. Built a square frame for the top and for the bottom. Then sandwiched the mineral wool between them with 4" corner pieces to hold them together. Then the whole thing was riveted together. For covering after that, I wrapped them with dyed muslin on the front, then a white piece for the back. Used hot-glue to keep the fabric on.
To hang them I used eye bolts and nuts and zip ties. Worked out really well. I also broomstick tied the front fabric to give a texture.
I can't remember what I paid for the Mineral wool. But it was like $1 for each drywall bead, $.69 a yard for the muslin, $10 in dye for the whole lot, hot glue and rivets, maybe another $10 for the whole thing. So it was really economical. I remember it basically worked out to being the same as the super cheap and crappy foambymail.com 2" stuff. But with this I get 4" for the same square footage and way better absorption and low frequency absorption.
Yeah I might be getting some reflection from the beading, but I figured that some reflection is still ok.
But I don't think you need pegboard or something for the back. With the beading, they rigid enough to move around. I use a couple as mobile panels and they work very well.
And from the video, those seem like they would be ok to move around as well. But if you are just hanging them, those will definitely work great and will probably take less time than mine did