I'm absolutely not a believer of this. It's beyond just their bad math. (It's an 8 minute workout) To do a proper sprint interval workout, you'd need to warm

I'm absolutely not a believer of this. It's beyond just their bad math. (It's an 8 minute workout) To do a proper sprint interval workout, you'd need to warm up (5 minutes at least), and go so hard in those 30 intervals that you'd need 90 seconds to recover. So 120 seconds * 12 + 5 = 29 minutes. Add in stretching and you're beyond a half hour. The other issue is many of these exercises won't get your heartrate up to the right threshold to be good interval training. Yes, it's better than nothing. No, it's not better than a real workout, and not scientifically valid.