On my last flight with 'extra' legroom it was pleasing to note that those pax who could not fit in the minimal pitch seats had indeed bought the extra space.
One thing we had been dreading was having Mr or Mrs Atilla in the 3rd seat in our row. I guess one strategy would be to book the left and right seats in the hope that no one would book the middle. Then offer them a window or aisle if they had booked that seat.