Sounds like Brad Pilon's Eat-Stop-Eat, the only difference being the 500/600 calories being allowed on "fasting" days (Brad recommends a 24 hour fast, stopping at dinner and not eating until dinner time the next night).
Although I don't do this style of fasting, I do the Leangains style of intermittent fasting, which is daily intermittent fasting, in which you fast for 16 hours and have an 8 hour "feeding window" (for example, I eat my first meal at 1 PM and my last meal at 9 PM, rinse and repeat.
I enjoy IF because it fits my lifestyle (I don't like to eat breakfast, and I like to eat bigger meals), but understand that there's nothing magical about it. This 5:2 style of eating seems to create a large caloric deficit, in turn allowing more freedom on the higher calorie days, which is great for adherence and helping someone actually stick to the diet without being overly restrictive.
If it fits your lifestyle and it sounds like something you would enjoy, give it a shot.