Ay sorry., I forgot you took over this training.
Okay. As I mentioned in my previous post, not every technique will make use of chakra to augment the attack, this being one of them.
Performance wise, its rather simple. The user will jump to head height whilst drawing his legs in, to the point where his knees touch his chest or are close to it, and swiftly kick the opponent with both feet in the chest. Its ability to break bones comes from the momentum generated by the legs when the user draws them in before suddenly kicking out, making use of the space in between to gain speed and force.
Seeing as its not very versatile, its battle usage is very limited. Personally, I doubt I'll use it. If I have to give examples though, I'd probably use it to create space between myself and my opponent if I needed to buy some time or instead of aiming for his chest, I'd target his face to break his nose or something along those lines which would hinder him severely. Alternatively, instead of jumping to head height, you could use it whilst descending from an elevated position to cause even more damage.
When up against such a technique, it opens the door to many possible defenses. Naturally the first thing you'd focus on is damaging your opponents legs so he would be hindered for the entire battle, if he ain't a med obviously. You could use ninjutsu that takes little to no time to perform in order to leave him vulnerable, eg, Nagashi. You could take the kick but, paralyze your opponent in the process. There's too many possibilities for me to list them all.
To me this isn't a technique that comes with advantages when using it, if anything, it seems like a high risk low reward type jutsu. Performing it means you need to be off the ground which means you can't move however you'd like in midair. Your movements become limited and leave you open to attacks from below, an earth spike or water pillars for example. At best, the only advantage this has is it doesn't require chakra to perform.