That's quite ingenious. I really like how it is done in the light ply.
I'm too much of a DIY guy to buy one but I could see this being a highly attractive field and bench accessory for a lot of folks.
And the issue of some added padding is easily solved by slipping a length of the split foam water pipe insulation over the edges of the "U". Just one long piece for a more open shape or perhaps in the case of the tighter fit as shown for the tail boom of that glider a short bit at the base and two longer uprights. A fix which would be easily added since that insulation is common enough at the home stores.