For those that use backpanel backpacks like the Flipside, can you give some thoughts on how the backpanel design behaves in different situations? For example, do you keep the waistbelt snug to help take the weight off your shoulders, and loosen it only when rotating it to front?? Do you keep it loose to make it easier to rotate it without adjusting? Would rotating it to front in loose or higher friction clothing be the snagfest I'm afraid of? Any other thoughts or considerations for making that process smoother and quicker? Thanks!
I use the Lowepro Flipside Sport 10L and 15L.
The 10L in particular works well as a trail running backpack for when my focus is a little more on training for races as opposed to photography. It's a little bit of an obsession of mine to never be without my camera gear, so the 10L allows me to pack a 70-200mm f/4 IS mounted to a T4i, a 10-18mm mounted to an EOS M (with lens adapter), an EF-M 18-55mm, 2 polarizers, and a Canon GP-E2 GPS unit. The fit is tight, but manageable.
When running, the backpack has to fit so that it doesn't bounce around - especially when running downhill. To achieve this, the shoulder straps and waist belt are fitted snugly around my body. When rotating the pack forward to access my camera gear, I usually have to loosen the waist belt slightly, especially when wearing layered clothing.
One thing to keep in mind about back panel access packs is that, depending on how much gear you're carrying, the backpack may not retain its shape when accessing your gear. It's a little hard to explain, but in my case, since I've maxed out the backpack, the sections closest to the waist belt become cinched due to the weight of the gear. As a result, it is sometimes difficult to put your gear back into these sections and difficult to zip the pack back up.
With the 15L, I can pack a 70-200mm f/2.8 II attached to a 5D3 or 70D, an EF-S 15-85mm attached to an SL1 (on it's side), a 1.4x extender, and another smallish lens like a 35 f/2 IS, plus filters. This configuration is too heavy to run with, but it works well for hiking.
I've been very happy with both backpacks. They're very comfortable and very durable. I haven't used the 20L, but it's basically the same pack, only larger, with more storage compartments on the front and around the waist belt. If the 20L performs like its smaller siblings, I don't think you would be disappointed.
Hope this helps!