Over the years, I've notice a lot of threads asking about BlackRapid straps. BlackRapid themselves have gone through several versions of their straps and I've tried to capture as many of them as I can in this poll (based on what's listed on their website and the models available from BH). Perhaps through our collective experience, we can aggregate some of our experiences with the straps.
This is by no means intended to be a BlackRapid fanboy thread. I've used several versions myself. In fact, I still use the Yeti strap and convert between it's single and double camera options. There have been previous discussion about caribiners or fasteners. Frankly, I've never had an experience except for once. I was holding my camera by my side and somehow I found that it had slipped off the caribiner. I can't fault the system, because I don't know if I had just forgotten to screw down the lock. It only happened once and that was many years ago. I don't have a tether, but perhaps I should use something... I'm thinking paracord instead of the tether kit that BlackRapid sells.
I have found the straps themselves not to stay in place forever. During use, I have no issue with the straps lengthening, but I have noticed that the more I take them on and off the straps will lengthen. For that reason, I've secured the straps with safety pins so that they cannot adjust by themselves. The armpit adjustment strap dangles annoyingling, too, and I've found that to be the same on every model I've used. The plastic secure for the excess strap length doesn't really work.
I'm 5' 7", average build at 165 lbs. I found that the RS-Sport felt more secure than the Sport Slim version. I got the Slim thinking that I could wear it underneath a jacket without looking like my shoulders were lopsided. The slim was just too narrow feeling on my shoulder. I'm now using the Yeti and it feels like the original Sport as far as I can remember.
I recommend the BlackRapid straps to everyone. They are pricey, but I like the fact that they have been in business for a relatively long period of time now and their products have worked for me.
Oh and I have a nifty looking MoneyMaker double harness from Holdfast. Their fasteners that fit in the tripod mount do not feel nearly as secure - their rubber washers even feel cheap. I trust BlackRapid's FastenR-3. I've not used any other version of fastener.
RS-4 Classic
