This is my first sling bag. I've had it for about a year and a half and I really like it. Before getting this bag, I used a Think Tank Retrospective 30. The Retro can hold more gear than I really want to carry on one shoulder and like shoulder bags in general, it tends to swing around easily when I bend or stretch to get a shot or grab my toddler.
The TurnStyle 20 forces me to be a little more selective about what I carry, which my shoulder appreciates. For me, this is a body + 2 lenses + 1 flash bag which is perfect most of the time. The wider end accommodates my 100-400 or 70-200 f/4. The middle end holds my 5D3 mounted to a shorter zoom such as the 24-105 or 17-40. The narrow end could hold a smaller prime like the 50/1.4 or 15 mm fisheye, but it usually holds my 580EXII. Re-moving at least one of the dividers would allow the camera to lay sideways with one of the longer zooms mounted. This all without a battery grip on the camera. The only way I've carried a gripped body is unmounted: 100-400 in the big end, body in the middle on its left side.
The bag sits on my left shoulder and is fairly easy to spin around under my right arm to access. When shooting, I carry my camera on an OpTech sling strap, also on my left shoulder, so it hangs at my right hand. I thought this would be awkward at first, but its surprising not. The bag goes on first so the camera's strap is on top.
The TT's strap is easily adjustable to accommodate different sized people, jackets, etc. Snug it up and its not going anywhere. The padding in the back is very nice and comfortable.
The TurnStyle can also be used as a belt pack but I have not used it this way. It has an iPad pocket but I don't use that either. Its handy for sticking papers in though. With a 70-200, 5D3+24-105, and a big flash, the bag is pretty stuffed so adding a 10" iPad is a tight fit.
I only have a couple of complaints. I wish the accessory compartment on the outside of the bag opened more fully. Access to the wide end of the compartment can be a little difficult when the main compartment is loaded.
This is the largest bag in the TurnStyle series, but I actually wish it were just a tiny big bigger. Not so I can carry more gear, but so access is a little easier. With the camera mounted to the 24-105, with the hood in shooting position, the RRS L-plate installed, and the large Hoodman eye cup, the zipper just barely closes. I know removing any of the accessories would help, but that's how I like my gear. So even an extra 1/2" would probably be perfect.