It's ok for shopping, but I wouldn't take it on a hike. The D-rings are at the back of the bag so it tends to tilt inwards when you carry it with a shoulder strap. I have attached some nylon straps to the top of my Camper which are useful for strapping stuff to the lid, but I mostly use them as a carrying handle. Off the bike the Ortlieb goes over one shoulder and the Camper is hand carried. The best thing is that I can fit the bike with the bags still attached easily in a lift or carry the whole thing up hotel stairs. Get the Longflap version as this massively increases the carrying capacity. I've used it to carry 2L bottles of soda and extra groceries back to camp. There's definitely a little bit of technique required to use the Carradice Camper successfully and you have to be a disciplined lightweight packer to make it work and I also travel with a small nylon back pack for emergency carrying capacity. FYI here is the Camper when I went to the UK back in 2009 and I was still using a support rack. I've opened up the longflap and I have my Tardis bike bag underneath it. I rode across London and left the Tardis at a friends house, but it shows what it can carry if necessary.
I find that my Ortlieb is a great off bike bag and easy to carry once the fiddling of getting the strap on it is done.