Coliff,
I've never used this type of ladder, only seen them advertised on web-sites.
I think they'd be fine for access (IE climbing over the odd gate), but not for day-in-day-out window cleaning where you climb a ladder over 100 times per day.
I think you'd be mad to use them routinely for window cleaning.
Get yourself a BS EN standard set of ladders. They're heavier than B & Q ladders, but much sturdier and you'll feel safer up them.