I have the Orion AW; it is the model from several years ago--I think the current model is a bit larger. Overall, the Orion concept is a nice one, but for me, it doesn't work for the amount of gear I want to take and I often end up taking my much larger and heavier backpack style bag.
I like the fact that the lower compartment can detach from the upper. I sometimes use it as a shoulder bag with a very lightweight kit. I find that the lower compartment isn't workable as a stand-alone belt pack--when loaded, it is just too heavy to be comfortable worn as a belt. It might be okay with a light camera and a single zoom lens and a few accessories. Used with the upper pack, it is fairly easy to detach the two sections and swing the belt pack in front, which lets you get your gear without putting the bag down in mud, sand, etc. Swinging it back to the rear is a little harder, however, as I always fumble to re-attach the sections. When both sections are attached and worn as a pack, I find it carries the load fairly comfortably.
With your kit, I think you would end up carrying the 70-200 in the upper compartment. You should still have room for a jacket, lunch, water bottle, etc. The rain cover only covers the lower compartment. The upper pack should protect things from an occasional light shower, but it isn't weather proof.
In theory, you can attach a tripod at the bottom, but I find it to be very awkward. I end up carrying it over my shoulder.