I've got an S Bag and frame, so have no idea about the O bag, just know @Apone, so could feel his pain.
I'd suggest to anyone with a brompton to get an S bag, as it's pretty much perfect for my day to day needs, and is large enough for me to do impromptu shops without worrying too much..
I've not tried anything else, but can recommend the Carradice Stockport bag. Keep an eye on the Carradice ebay store, some factory seconds come up on there. I think mine had an extra rivet thing on it, it's been awesome and waterproof.
I've got an S Bag and frame, so have no idea about the O bag, just know @Apone, so could feel his pain.
I'd suggest to anyone with a brompton to get an S bag, as it's pretty much perfect for my day to day needs, and is large enough for me to do impromptu shops without worrying too much..