so is it really not beneficial to run a cetane boost?
Depends on what type of return you are looking for on your investment. A lot like Premium gasoline compared to the low octane rating stuff. The cost of the higher octane gasoline just doesn't make sense, as there is not enough of an increase in mileage.
Few people report noticable mileage gains to increased cetane. See what works for you. Take careful note of your driving habits for one tank of fuel and record your mileage. Run another tank of fuel with the cetane boost, trying to drive in the same fashion as the previous tank, and compare mileage.
Just because cetane is negligably increased, it will not make huge difference in BTUs. the biggest influence on mileage is driving characteristics.