I had plans to extend my Megacab earlier this year, I went back and fourth with the place in Utah (second vid you posted) for several months. I placed an order for my 1172 and was waiting for that to come in prior to extending my truck.
To make a long story short, the company who did these mods quit doing these mods about a week before I was about to come down. Their reasoning was that they were having some issues warranting some of the old extensions were done before. Not sure exactly the details but that is what I was told.
BTW, the company was resold several times since they started doing these conversions several years ago. I was told the original guy who started this in Utah is now still doing them still somewhere in Utah.
I did run into a guy in the desert who had one of these extended and almost 70k on his and he had no issue with his, I believe his was a 2010. It was beautiful, it had a lift on it with 20 inch rims 37 inch toyos and EXTENDED.
I since I had to buy a new long bed truck and now have both.