Monthly cash flow vs. 50% rule cash flow

[Brandon Lancaster]

When I run the numbers on a multi -family  through the rental property calculator It spits out a monthly cash flow number that is 4× greater then the "50% rule cash flow" estimator. I'm ok with the first number, but the estimator makes me rethink whether this is worth it or not. The numbers are a massive difference in my mind. Please help me wrap my mind around which number is more accurate. I'm new to investing and appreciate any direction or guidance on which number to believe to be more accurate.