It’s just a very low calories diet not a fast. If you are eating or drinking calories you are not fasting. For benefits you will lose some weight that way. But you will likely feel like shit. I would rather eat nothing than eat 500 kcal a day. Fasting moves you into ketosis which once you switch from burning mainly carbs to burning mainly fat is easier to manage. This will keep bouncing you in and out ketosis making you feel horrible.
Compared to what? Somebody doing a 21-day fast which if done right it is not harmful?
And beneficial how? I mean what are your goals?
Also that doesn’t look like a fast at all, that looks like a calorie restricted diet. I just finished a 4-day water fast and I would do that twice over before I put myself through the feeling of starvation that eating 500 calories a day would give me.