Yup. Almost everyone does the flop. There are probably some people who don't, but almost all serious high jumpers (university and beyond) use it. The scissor kick and the roll have some pretty serious limitations and also make it easy to get hurt. One of the chief advantages of the flop is that it allows for a better transition of forward momentum into a vertical leap. I was able to get my hips above six feet in high school, no sweat. I believe that's starting height in college. Unfortunately, to do the flop properly takes a lot of practice and coordination. Because of the motion of the flop, I often ended up hooking the crossbar behind my back as I went over and landing on it with my arms awkwardly pinned. Also, as soon as your back clears the bar, proper flop technique necessitates what is often referred to as "the mousetrap" where the jumper folds like a book. Woe betide the jumper who doesn't work their abs. I kind of miss athletics.