in answer to your question , yes echo will clean the frames.
i was taught by my old boss , an old hand twenty years ago ,that if i wanted to be a proper window cleaner i would wipe over the frames and cills as well as cleaning the glass.
now twenty years on i am still 100% traditional and still wiping the frames and cills
your lucky your customers are paying you extra to spring clean the frames.
i make it clear when pricing that the frames are included hence my prices are higher. in reality it barely takes a minute to wipe over with a damp scrim followed by a quick buff with a dry scrim. month in month out .
the result is clean frames that only need a wipeover
when i take over from a glass cleaner , as opposed to a window cleaner, its a difficult job to get the frames gleaming and can take many cleans, i always explain this at the start
when i started building my current round i had customers approaching me as they had seen me clean the frames and their wc didnt, they would rather pay the extra as they can see the difference it makes to the outward appearance of the house
its usualy the woman of the house that decide to have a wc and its the houseproud that feel you are worth what you charge every month