Yeah, I've got a whole system that I bought to carry Nikon stuff around. It's extremely well-made, and though I don't have that exact bag, if they say it's good for a Leica, it probably is. It's a dedicated system: the bags are made to go on a padded waist belt, and are hooked on by a kind of metal-clip system with special clips on both the belt and the bag. Once on, they won't come off accidently; you could fall off the Matterhorn and you wouldn't have to worry about the bags coming loose. They have a wide range of bags, for carrying all kinds of stuff including water bottles, CF cards, rolls of film, accessories, etc.
I don't use mine anymore. For one thing, when you're wearing it, you look like you just jumped out of an airplane: the airborne ranger look...like you're carrying a weapons system. The belt's four inches wide and heavily padded and where I was working at the time I bought it, hot. And when I was up north in the woods, it got hung up on brush. And as I said, when you're downtown, *everybody* looks at you. Probably work okay if you were in a bullpen with a lot of other photogs, but in that situation, a vest is probably just as good. If you decide you want to go with it, I know where you can get one cheap. 8-)