if you are only promoting regular window cleaning on the leaflets, i would not be sure what the uptake will be.
it could be good, normal, better than normal, or worse. i dont know
but i think if you do one off window cleans, and advertise one off jobs too (jet wash, gutters, etc) then i am confident you would see a good enough return or better.
people are booking in big ticket jobs at the moment with us so we're planning on starting leafleting for them