Okay ... it works like this. For me its as follows:

Out runners: fit 'nicer', easier to use, no gears to strip, limited prop range, no bent shafts when you nose over, plug and play!

In runner: more efficient, varied range of prop sizes, gearing allows user to control amp draw etc, can be lighter if correct gearbox is used.

At present I only use Out runners as its convenient and I know what props I want for which plane. Himax motors are nice.