Its not a formula for success, its a formula for prioritizing what to build (success is more than prioritizing features) and it relies on at least one value (the d in the formula) which is not easily quantifiable.

Its essentially a variant of the standard formula for prioritizing work effort in any software project that I've seen in many works on Agile and Lean methods, which is basically v/c, where v is the business value expected to be produced by the change (and usually the hard part to reasonably estimate), and c is the cost of delivering the change. (The b × d that replaces v in this article's version is an interpretation of what produces business value in a property with multiple customers, but, given the fuzziness is d, retains the difficulty of the base version is assessing expected value.)

I'd also suggest that the formula considers only the value to existing users, and not the value of a change in growing the user base, which may be important, particularly in the context of a startup.