I've had my Heatwave Messenger Bag over 6 months now and have been quite satisfied with it. Because I bring two meals, paperwork and additional items to work each day, I needed the larger version of this bag. It's pretty heavy when loaded (my fault-not the bag's), yet is comfortable when draped across my shoulder. The material has been durable and it repels rain adequately in the walk across the parking lot. I like the small amount of extra material on the zipper top, which has allowed me to fit things better. Would like to see a two-way zipper, though.
Two minor negatives: The carrying handle is comfortable to hold, but is placed off-center, which makes the bag list to one side when hand-carrying. I've also had some problems with the shoulder strap slipping out of adjustment from time to time. This may be due to the heavier load, and has not been a major issue for me.
I'm a teacher and I need a bag to carry thick teacher guides, papers to grade, lunch bag, etc. The material seems durable. Under the front flap is a clear pocket for ID, a mesh zip pocket for keys, and several zip pockets for my flashdrive, pens, etc. It makes finding those small items very handy. I ordered the large and it feels so unwieldy, even when 1/2 loaded. I'm 5'6', and I have the strap adjusted to the shortest length. It just hangs too big for me. (Maybe the bag would work for a taller person.) I'm now ordering a medium, because I do like the bag's features.
My son is a senior in high school, and he carries a lot of heavy books, and often does not have time to go to his locker between classes. He got fed up with backpacks a few years ago and I started buying him messenger bags. it was very hard to find one big enough, and each lasted only a few months, by which time it would be either shredded on the bottom or ripped out at the points where the strap joined the bag. enter the LL Bean heat wave bag---we bought the large one and it's GREAT! So far it has been in use for three months, it is showing no wear whatsoever and it's plenty roomy for all my son's school stuff. LOVE it. I'm buying another to keep just in case because it's on sale at the moment!