I used to own a Slingshot (a 300, I think). The bag did not distribute the weight of my equipment very well with only one real shoulder strap, causing an ache in my back and shoulder when I hiked. I actually hiked to the top of Mount Washburn in Yellowstone with it -- and that trip convinced me to get a real backpack. The Flipside design works much better for me -- I can carry more equipment with less strain now. BTW, I think the resurrection of this thread was a good omen. I sold my Flipside 500AW to someone on POTN.com (a photography forum for Canon shooters) who contacted me out of the blue. The 500AW was just too big for my needs -- the 400AW is as big as I can use for airline travel and hiking.