I had the one-holster version 1, which I still use from time to time, but the Dual-holster version 2 is improved and it's really nice to be able to have my 24-70mm lens on one camera, on one hip, and my second camera with the 70-200mm on the other hip... no more lens swapping, I can shoot pretty much everything I want with either of these cameras.
I haven't had the chance to go hiking yet with the new holsters, but that is what I really like about the Spider holster, you can go hiking in trails, the countryside, walk all over the city, and have your camera(s) with you at all times, and they're never in the way, your hands are free, I can't imagine being without my Spider belt/holsters. If ever I do end up without it (never for long), I'm always looking to holster my camera on my hip, out of instinct, and it drives me crazy not to be able to get the camera out of my hand when I need to.
Dragging my cameras on any kind of straps seems nightmarish, well, for the amount of walking and jogging that I do, in any case. For more sedentary photographers, that might not be as much of an issue.
I've been using Spider for eight years now, and there is no better system.