Welcome.
There is a lengthy discussion on about OOP in the Tandem forum. I stay in phase for two reasons:
– We have lots of potholes where a butt break is interesting.
– If we were OOP, I'm almost sure I would drag a pedal in low spots; in phase pedals means one less thing to consider.
However, I have put my stoker's cranks two teeth ahead of mine. That way, if/when she stops pushing abruptly at the bottom of her stroke, my knees are still pushing and therefore are at a less vulnerable point. My stokers are 11 and/or 7.