I bought mine from Williamson Pumps - a year ago next month - it's had some hammer, but is still going strong.
I've had to replace the battery (£5.00 from Motorworld; it's the same battery used by electric scooters) and had to patch a hole with some resin based putty (£5.00 from B & Q); other than that no problems.
It's a robust bit of kit. I use it constantly; every day I work, but I have a spare one just in case.
It's great if you're on a budget, or just want to dip your toe into the WFP world. My next major purchase will be a van with a WFP system; but I bet I still use my backpack on much of my residential round.
It also costs a fraction of the price of a Freedom Trolley, is much much lighter; therefore more versitile and allows you to work comfortably out of a standard car.
My point is, since it's a well made bit of kit, it may be worth purchasing the cheaper US Ebay backpack at £170, rather than paying £270, which some suppliers are charging; mentioning no names.
PS.
The hole originated from a tiny crack I made when I dropped the backpack. I tried to fix it by heating up a knife, till it was red hot and smoothing over the crack.
This didn't work and made a hole; which was a lot worse.
So I put this resin based putty on it and it's been fine since.