Tough to take everything into account, but I find it troubling that all non-success/failure outcomes are not part of the calculation (ex: 8-yard gain on a 4th and 10; a fumble on a 4th and 2 run, etc). It simplifies the formula to the layman, but I have to imagine that it adds enough additional variance to matter, especailly considering we're talking in variances of less than half a point in their stated example.

Also (and to their point), there is a ton of variation between offenses, defenses, punters, running backs, etc. Using this as a rubric is a nice idea for a rule of thumb for an armchair quarterback, but I'd strongly disagree with using it to accurately criticize any decision within a couple points of expected value.