Unless you have actually used a Black Rapid type sling strap, it's hard to know how good they are. The key to it, apart from the sliding sling aspect, is the camera hangs upside-down, by a single rotating attachment point. The OpTech is not like that (I'm guessing, for patent reasons). It's worth getting a cheapy like the Q-strap or similar just to try - they're only a fiver on Amazon - see how you like it. Just check the security of the stitching and reinforce that if necessary and they're okay. They're not the same quality as Black Rapid, but most problems with this kind of strap are basically user-error when something comes undone.