Zeus,
Hard to say really, iy doesn't have to be a trolley, it could be a backpack or van mount.
Anywhere you can go with a ladder, you can go with WFP, you do have to adapt, even change your way of thinking with regards access! No, really, if you have been going 15 years you will have your modus operandi grooved so smoothly you won't even think about it
Of course if you are walking from your home and carrying your equipment with you for 80% of your work, then that would have to change, no way on earth could you cart enough water with you
But in operation itself, even an ineffecient WFP'er would be 25% quicker.
And quite regardless of all the obvious safety benifits, it's so much EASIER too.
I don't personally think the WAHD is going to cause the average domestic window cleaner any problems for some time yet (insurance claims notwithstanding) So you can probably continue using ladders in time honoured fashion.
Unless you changed the way you work and worked directly out of your vehicle for all of your work, then you are probably right, WFP would not suit you.
But if you do have clusters of houses close together, then WFP is very effecient.
It's when you have a small, stand alone account that their is no improvement on the time it'll take you to do the job. (It's still easier though
)
To see if you would like it enough to change your entire work patterns, see if you can tag along with a WFP window cleaner for a morning, you wouldn't have to use it, but observing an experienced user negotiating gardens and obstacles would certainly give you a much better idea as to whether it would be suitable for your own work.
Ian