If you intend to clean them trad on the 1st clean then change over to wfp afterwards, you will still have the same problems as if if was a 1st clean with wfp.
These type of frames hold loads of dirt in the gaps of the frame, as soon as water hits this dirt it runs straight down, so it does not matter how many times you trad clean them, as soon as a wfp is used and all this hidden dirt will run down from the windows.
Next these windows are more difficult to clean but not impossible, what I do is on a 1st clean I change my brush over to an old one I only use on very dirty 1st cleans, this stops my regular brush head becoming contaminated.
I then really scrub the frames down, while jetting plenty of water into the cracks, after this is done I wait for about 15 minutes untill they stop dripping water, I then change the brush head to my regular one and then clean the glass.
I follow this up with plenty of rinsing.
On the next cleans I don't have to worry too much about the frames because they are still free of major dirt, a quick clean is normally ok for them.
If you are going to clean them trad or wfp, you need to be careful about the amount of people who are moving around your workng area, you don't want them knocking you off your ladder or them tripping over your hose.
Also with wfp cleaning, you have the added problem of the water dripping down onto the shops customers and also onto any shop fitings and stock which most shop keepers kept outside their shops.
I would either clean them very early in the morning or on a sunday.