Safety
You are striking at full speed while looking at a screen. A minute of setup prevents most of what can go wrong.
Your space
Clear about two metres around you in every direction, including behind. A round kick travels further than most people expect, and you will be watching the screen rather than your own foot.
Look for what is at head and shin height: table corners, door frames, light fittings, television stands. Bare feet on a hard floor grip badly during a pivot — either train on a mat or keep your feet still while you turn.
Put the phone or laptop on something stable, far enough back that your whole body is in frame. Never on the floor in front of you, where a kick will find it.
Nothing to hit
The targets are on the screen, not in the room. Do not strike furniture, walls, the device, or another person. Striking a hard object with an unwrapped hand is the most likely way to injure yourself here, and the game scores your movement — not contact — so there is nothing to gain by hitting anything.
Your body
Warm up before a fast round. Kicks and knees from cold are how people pull a hamstring or a hip flexor.
Stop if you feel pain, dizziness, faintness, chest discomfort or shortness of breath beyond normal exertion. Rest and drink water between rounds — the game keeps offering another one, and it has no idea how tired you are.
If you are pregnant, recovering from injury or surgery, or have a heart, joint or blood-pressure condition, speak to a doctor before using this. It is exercise, and fairly vigorous exercise at that.
Children
Children should use this with an adult present, in a cleared space.
What this is not
A game, not coaching. It scores timing and movement from a camera, which is not the same as good technique, and it cannot see whether your wrist is straight or your shoulder is where it should be. It is no substitute for a qualified instructor, and nothing here is medical advice.