I got this bag from their rep at Outdoor Retailer and started using it immediately. It's very packable and light and has a lot of room inside. The straps are at a good angle to hang from the back of my chair and the sternum strap helps hold the shape if you can handle the extra lump of the buckle on your backrest. It's small, but it could be an issue for some people.
This is a great bag to have with you to stuff your coat or outerwear in as its large enough and waterproof. To put it back into it's carry pack configuration, just stuff it all in and zip it up.