I bought a Lowe Alpine Air Zone Trail 25 abiout 3 years ago and I’m broadly pleased with it. I take no care of it whatsoever yet it’s still in pretty good condition. The Air Zone feature (a stand-off gap between the pack and your back which is supposed to reduce the ‘sweaty back’ problem) does work to an extent, but certainly not completely. Then again I’m a fat sweaty walker so I can’t imagine that anything would be completely successful at this. Off the top of my head my two minor niggles are i) that the pouch on the waist strap isn’t quite big enough for my Garmin GPS, so getting it in and out requires a lot of pushing/pulling and the fabric is starting to show signs of wearing out and ii) that the stretch cover which is supplied to protect against rain showers is water-resistant rather than waterproof. It helps a lot, but since it’s only worth getting it out when the rain starts properly why not make it completely watertight (weight maybe, or durability ?) ?
I checked it out in Go Outdoors against Osprey and one other (can’t remember which) and for me it was the comfiest of the three (I took water bottles, torch, wet weather clothing etc to pack inside for a weight test). Plus GO had an offer on it at the time. I did buy it from them although again I might have been able to save a few quid if I’d gone online.