I did a first clean yesterday, and what a pig of a job!
The windows had some sort of black couloured residue on them, that didn't want to shift, so cleaned them with an applicator and hot water before using the pole, and although they cleaned up pretty well (first clean in at least 10 years apparently!) I am less happy than the customer.
I plan to buy a porcupine to have another go, but if anyone has any tips, they would be welcome!
I charged extra as it was apparent how filthy they were before I started, and she has not (yet) committed to further cleans, although i think it's fairly hopeful.
Location is London, and near a main road, so plenty of air polution.