Much as I love Ortalieb gear, I have 4 of the panniers and the rack bag, I've never been impressed with their bar bags, have yet to find a bar bag better than my one from
Altura,
It only has three design faults, it's not waterproof (but does have a cover) and it has no mounting for lights and the map case could be 5mm bigger to fit a O/S map easier
What makes it better than the Ortalieb is
It has two external mesh pockets, good for compass, tissues, whistle, snacks
the strap can stay on the bag when its on the bike
It has the standard R&K fitting so clicks on off very easily and is transferable
It has 3 internal pockets (great for money, phone, keys etc
The lid has a big internal pocket (good for about 3 x OS maps)
The lid also has a transparent map pocket which is not removable
Main section and lid are both zipped
and most critical, it opens facing you on the bike.
It is also small, which stops you overloading it, as it is imperative that the bar bag only holds what is valuable or is needed whilst on the move
Basically as long as it will take a SLR, a map and a couple of sarnies and a rain jacket, that is big enough
