Most adults burn 400–600+ calories in a 60-minute Cardio Tennis class. That's comparable to a tough spin class and significantly more than a steady-state run for the same time.
The format works because it's interval-based: short, sharp bursts of effort with brief recoveries. That style of training is well-studied for fat loss and metabolic health.
And — crucially — people stick with it. The single biggest predictor of weight loss is consistency, and Cardio Tennis is genuinely fun enough to keep coming back to.