Re heat: Actually, this is great pack for those in hot weather. A highly sweat-prone person like myself will probably find the DLBP more comfortable to carry around in the heat due to the lack of padding. I carried my S19 in 33 deg C/93F weather a couple of weeks ago and my entire back was soaked after 15 min . . .
All in all, a nice compromise between a 'proper' backpack and the lightweight packing cubes. I'm a happy camper~