They look good. I made a target box that has a duct seal backing and its advantage is that the mess from paper and pellets that hit directly on top of each other is caught in the box. The duct seal it self only needs to be about an inch thick to stop even the most powerful airguns. When it fills up Ive managed to clean out most the pellets and beat it back into shape and keep using it.
If you cant build something yourself then those look pretty good and not crazy expensive.