Hi,
just a little input frow a relatively newbie,

i started last autumn, trad, then went wfp around xmas time,
as the backpack was the cheapest option, i went for it, and in my opinion it was a good starter, but humping all those 25 litre barrels about all day ,for filling it etc, bacame an absolute pain, hoping the darn thing had enough water to finish the last window, (and it never does)... either dragging it around or being uncomfortable with it on your back.
but that was me starting out without any other gear,
so thats my opinion as a starter upper,
but i totally agree its good for awkward places and an odd use here and there, and it certainly will be easier for some of you guys who have all the taps, pumps and van tank on hand to make things simple as regards to filling it,
and i can hear you saying, its nothing carrying a backpack all day, or its easy filling it with 25 litre containers...., yes it is easy, its just time consuming and a pain to be honest.
so yes it is the quickest, for an odd house. OR......
if its used as a back up or unless you convert the damn thing to a trolley or fill via pump, ( even thats a pain )..
whinge over

Gary.