My arkel handlebar bag has travelled with me for 6 years and shows no sign of wear... I'm still very happy with it and extremely happy with Arkel's service and communication.
I like the smaller Arkel bag because it forces me to discipline what goes into it: wallet, camera, cell phone, GPS, sunglasses, journal all fit nicely. The metal-on-metal mount system makes it easy to take the bag off so my valuables stay close to me, but once the bag clicks in the mount it is very solid.
The map case on the smaller bag is not 100% waterproof like on Arkel's larger handlebar bag, but it's been fine for me, ACA maps fit without any trouble.
For light rain, the bag is water-resistant. I find the rain cover easy to pull over in case of downpours, and also easy to lift up to peek at the map.