I have a Black Rapid RS-7 and I have a BosStrap. I loved the Black Rapid until I found the BosStrap and here's my take on the two of them.
The Black Rapid: The RS-7 I have is built like a tank. I am not *even* kidding when I say this. The construction of the BR is both a strong point and, in my opinion, a weak point. It's almost too much of a good thing, it's stiff and bulky. That being said it is very comfortable to wear and the cross-body design is the bomb. The RS-7 attaches to your camera using the tripod mounting socket and that means you will need to have a Quick Detach (QD) plate attached to your camera when using the sling. If you remove sling, the QD plate is still there. If I set my camera on something, like a table, the QD plate made it "wobbly" and prone to dinging and denting surfaces it sat on. I found these issues annoying. I also did not like how the camera hung at my side using the tripod mount.
The BosStrap/BosTail: The BosStrap is both thinner and lighter than the Black Rapid. It's made of the same material as the seat-belt in your car. The strap I have is the wider of the two they offer at 1 1/2". It folds up in your hand neatly and is nowhere near as bulky feeling as the RS-7. The BosStrap is also cross-body and very, very comfortable to wear. The BosStrap is designed to be used with the BosTail but I don't like the BosTail so I removed it and instead use a carabiner rated for 20 lbs. This carabiner hooks through the connector on the BosStrap as well as through the strap mounting lug on my D7100. Removing the strap requires unhooking the carabiner from the strap lug, leaving my camera free of any kind of attachments. It's fast, fast, fast to connect/disconnect and requires no additional parts. The camera hangs differently from the strap lug than it will if you mount from the tripod socket. Which you prefer will be a matter of personal taste but I simply prefer the way my camera hangs when using the BosStrap.
Both slings make carrying your camera sooooooo much more comfortable and they leave your hands free. Once you try a sling-strap you'll NEVER go back. You'll laugh at the concept. You'll wonder why it took you so long to discover just how awesome sling-straps are. It will change your life. It will whiten your teeth and make you more attractive to the opposite sex. A sling-strap will improve your car's gas mileage and freshen your breath. It could, quite possibly, save your marriage.
Just my two-cents.
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