They’d probably get the same result. Or someone could put on a pair of running shoes and then walk/run stairs doing 8 second intervals every now and then. That is free if you have running shoes. One could also find a hill in a park and run up and down it doing HIIT intervals on the way up.
I have no problem with untrained people doing HIIT to stay fit. The exercise science shows that it works … to a point. And then you need more stimulus to improve further. You are never going to win a bike race riding 8 minutes at a time.
But for people that otherwise do no exercise, 8, 15 or 20 minutes of HIIT per day sounds like a fine workout. One doesn’t need to pay 3000 pounds for the privilege though.