Transient Bags making tweaks to the design for the past few weeks. I still have the prototype, which has been great, the tweaked version im sure is the best sling bag for heavy duty messenger work. Check out his site, he has a great write up over there.
"To kick things off, we will be releasing our first model of courier bag in 3 sizes (Small, Medium Large) falling into a retail price range of $130-$170 (with a 20% discount to you working couriers out there). Full Product specs will coincide with the launch, but let us just say that we are quite happy the end result of these bags."