After reading TC's interview quote, this is the conclusion I've come to.

The EZ-EFI needs to know a target AFR, with out a dyno or a few runs down the drag strip for some mph's, you aren't going to know the ideal AFR the moment you bolt it on the engine, UNLESS you just dyno tuned it with something else (carb, etc) and already know the ideal AFR target and tell it, then of course it'll magically make the same number almost right off the bat. First run to see where the AFR is, second run to put it where it's ideal.