Simon, I agee with your post, however would you rather trail round nine-stone of dead weight, or four-stone of dead weight?
The only thing that puts me off a Freedom is the dry weight of it.
I've also got a 50 litre system, which must weigh just as much as the Freedom, only loaded with 25 litres, but my 50 litre system holds double the water capacity and is capable of carrying 30 meters of hose; at least.
Given it's weight, water carrying capacity and versitility, I don't think you can go far wrong with a backpack. Sometimes I put it on a trolley; other times I use it as a grab-and-go.
If you want to get into WFP and you're on a budget; I think the backpack is the 'nuts'.
This year I'm hoping to get a van-mounted system, once I pay off my tax and council tax arears!