The point being that too rich is good - too lean is bad. You won't hurt the engine by running it too rich for too long. The opposite is not true.

Today's engines are not all made with the same level of quality and finish from brand to brand. This further complicates the matter of ringed engine break-in times. OS engines appear to require the least amount of break-in time while running blubbery rich. I am not familiar with Irvine's philosophy, so I would follow their instructions to a tee, so to speak. Truthfully, I follow the manufacturer's instructions regardless of my familiarity. It's just good common sense.

Since engines that are running rich are producing less power, it might be wise to select a model that flies well on the reduced power so that the engine will not be tempted to lean out the engine to make the model fly better. I usually have one such model in my stable, set aside just for breaking-in engines and testing new/repaired radios.