Hello Jinky,
I no your not getting at me and its a good question, firstly let me say i would be one of the last people to knock the freedom trolley as your right it is a wonderfull piece of window cleaning equipment.
The reason i use the backpack instead, is more to do with the way my round is, than it being a better tool.
I dont have many houses in a run as you would say, and infact there are only about 4 or 5 closes where i might have half a dozen jobs, and a lot of these have garages so i have to climb over, and if i left a trolley out or my pick up open round here while i was out of sight they would be gone!
As regards weight i dont have any problems in climbing over things or carrying it when its full.
Its like you said you use the tool to suit and in my case its the backpack and the trolley stays redundant, however its always there should my situation change or the need to use it comes about.
I have answered your question as honestley as i can Jinky, hope this helps.
Ron.