I have a Carousel saddle pack that I purchased last spring and so far have been very impressed with the durability. I think it's a medium and I fit a camp stove, sleeping bag, tools and even some food inside the thing. I wish I had ordered the handlebar bag as well but ended up holding off. Just be sure to order it well ahead of time so you get in the queue and ensure it arrives in time for your trip. Jeff was very up front about the lead time and delivery, so I wouldn't say I experienced any delivery issues. Then again, being a one man show, I suppose it could happen in an unexpected situation so I'd be prepared if timing is tight.
These bags really benefit on the rough terrain where racks would take a beating. They are designed to be lightweight, durable, and to hold that absolute minimum amount of gear that you'd need in the backcountry. The other thing is they are pretty low profile, so it's nicer than a rack/pannier setup when shouldering a bike through a spot that isn't ride-able.
For road touring, I'm sure they would work, but you probably sacrifice some of the organization/space benefits that you get from a traditional rack and pannier setup. A bar bag would probably make a nice complement to an already existing rack setup though.