Ya, that definitely looks like a bad idea. Learn the pistol squat progression, starting two footed and building mobility then work your way into one legged descents till finally your performing the full one legged squat with your free leg straight in front of you. You can have the whole thing together in a couple of months and it will take you much further than these weird chair things people are doing.
I've never done those before, but I get in the same position then to what's called a split squat. Basically a lunge with your back foot up on the chair. I usually have to do set of 40-50 of those with each leg. Killer workout for your a$$.