I once bought this one
and used it on my touring bike while still using my aero bar.
Advantage: Unlike normal handlebar bags it moves the weight close to the headset with the result that you almost cannot feel the weight. With a 100 mm stem and then the handlebar brackets further extending the weight outwards and away from the headset you really feel the added weight and steering becomes more sluggish.
Disadvantage: As a bag for my mini front rack, I used a small 2,5 litre Ortlieb roll. I would roll up the bag and let the two ends wrap around the aero bar on the top and close with the quick release buckle. So the aero bar made sure I would never loose my bag, however the bag was not really fixed sideways on the bottom, and I hated that.
I would be happy to receive suggestions on a proper multicompartment bag for this mini rack :-)