Absolutely a horrible and unsafe design. Terrible quality.  For starters they are dangerous. I have been using inversion boots for decades. These have a very shallow hook design and are on the wrong angle to hang safely on any type of bar. They unhook from the bar very easily while pulling your self back up. Plus the angle is so off on the boot itself that they dig horribly into the back of the calf muscle. Again, I have used different types of inversion boots for years and years. There are terrible.