Let me be honest - these boxes won't win any awards for sturdiness. The cardboard feels like it's barely thicker than a cereal box when you first unpack them. I actually laughed when I saw how thin they were compared to professional moving boxes.
That said, they did surprisingly well for my framed 36x48" artwork during a local move. The key was using about half a roll of packing tape to reinforce all the seams and corners. I also sandwiched each piece between layers of bubble wrap before boxing. The adjustable flaps were handy for getting a snug fit.
Where they really shined was transporting flat screen TVs. The 40x60" size perfectly fit my 55" TV when laid flat. Again - tape is your friend here. I wouldn't trust these for heavy mirrors without serious reinforcement, but for lightweight framed items and electronics, they get the job done if you're willing to put in the extra padding work.
Pro tip: Buy these when they're on sale. At full price, you're better off getting heavy-duty boxes from a moving supply store. But for occasional use with proper precautions, they're a space-saving solution that beats wrestling with awkwardly sized items.