I would be very surprised if 500 kcal didn't register because of IF.
Is that the claim though? I've been doing 5:2 for years and there they say "eat normally" on the off days. Don't overeat/compensate.
So intermittent fasting for ease of compliance? Yes, that I agree with. As stated above my issue is to let people believe they can eat all the food they want as long as they follow a magic schedule.