I pay about £70 which includes "property being worked on" Property being worked on means the actual item you are cleaning. If you don't have this cover then the "item" or window you are cleaning will not be covered. However, should your pole fall & break the next window (which you were not working on at the time) this will be covered. So, everything else around you, which you are not working on, be it another human being or someone elses property (item) will still be covered without the "property being worked on" extra cover.
However, in my case the "property being worked on" is burdened by a £400 excess so domestic window wise would probably never be used.
This is often confused by people thinking that "property being worked on" means the whole of the customers property- it doesn't.