In my experience (40+ years) the only ladder window cleaners should use is the so-called 'A' frame (proper name 'Tree bottomed point')
They were designed by window cleaners for window cleaners long before most of you were born.
Properly used they are far safer, more stable and more versatile than 'open ender' ladders.
Unfortunately there are very few of us left who have had proper training in their use by people who knew what they were doing.
H&S even refuse to acknowledge their existance - hardly surprising, they come into the category of 'long before they were born'
If the H&S were to instigate proper training in the use of the correct equipment then there would be a dramatic reduction in the number of falls occuring in the window cleaning industry.
Rant over
I retire in December - one of the last of my breed