My husband just bought me the Arkel big handlebar bag as an anniversary gift and I have some reservations after searching through some of the posts. It is a 10 L bag and once I fill it I am wondering if it will create a steering problem. I like the idea of quickly releasing the bag and being able to carry it around with the shoulder strap. I am not interested in a trunk bag because I don't feel like fiddling around with velcro straps, etc to take it off and put it back on. I already have panniers and I guess I could use one of these instead of the handlebar bag. The smaller Arkel handlebar bag is nice but doesn't have the same features as the large one. Ooo, please help. I just can't decide!
A handlebar will not create any handling issues since their not design to carry a lot of weight anyway. I have a large handlebar bag for my road (racing geometry) bike and the bag creates no handling issues.
The biggest problem with a handlebar bag is the inability to attach a light to the handlebar; but Minoura makes a special T bracket that can extend upward so you can mount a light or computer to that. But handlebar bags are very useful because you can get to stuff like food or a jacket without having to stop the bike; also most medium to large handlebar bags have a clear plastic top for maps making in nice to use while riding and viewing a map at the same time.
As far as a large one vs a small one depends on you and how much stuff you want easy and fast access to. Some smaller bags don't have the map pocket though.
Bar bags are really useful. I have used mine with rear panniers on tour and have tackled some technical off-road descents with no problem.
Beware interference with STI cables. Beware putting a wide bar bag onto narrow bars, you still need room for your hands.
My Carradice bag has a 5l capacity and I dont see the need for a larger bag.