Hi,
for me the large handlebar bag is too small. (You never can have to much space)+
Rollers/Packers:
I have the Packer (but the first version). The external pockets are very useful, but if the bag is fully packed the space of these pockets is limited. This will change if you buy the 2009 series.
The PAckers are also waterproof and there is no ventilation. I won't cycle with open bags.
You also can buy external pockets separately (or both system)
Thomas