Having used both backpack and Freedom trolley they are both excellent for wfp.
I started out with the backpack and found i was wasting quite a bit of water tipping it in but thst just might be ne being cacky handed. Also time consuming filling it up as it doesnt hold much water, i still use it for some hard to access areas plus it needs charging every night and it is much noisier than the Freedom trolley ( not that this is an issue). Ladders make noise :
What i find i like about the freedom trolley is you can take your 25ltr container straight out the car on the trolley and away you go. No wasted water and no time filling up, does not need to be charged up every day the pole holder gives you somewhere secure to hold your pole to save laying it on the dirty ground plus when pulling it along it gives you a free hand.
I find the construction of it has been designed for ease of monuvre, going up and down steps is as easy as taking the backpack.
I am awaiting delivery of the add-on to carry another 25lts of water this will ideal on big jobs.
I personally think its worth paying the extra money for the freedom trolley as i think it will last for years.
The time and detail that gone into designing the trolley have obviously paid off, the end product is " brilliant"
The main thing is its helping me earn more money safely and eficently.
At the end of the day its down to personal preference and affordability
Your choice the backpack, Freedom trolley or Matts diy site or big companies and pay the extra. I looked into it, did the research and ive heard nothing but good comments since so it looks like ive made the right choice for me .
Brett.