I used to just carry my cameras on independent camera straps, but when covering games and/or long days with two cameras, a dual harness prevents hunching your shoulders trying to keep your camera up.
You can go less expensive and buy a generic $20 harness on Amazon (it's cheap construction will show quickly, or a more expensive leather one (I'm really just not stylish enough to pull this off).
I admire Peak Designs build for many camera straps, but as they don't have a dual harness, it's not a system for me.
I love that the OP/TECH easily exchanges between other OP/TECH straps for when I just want one camera and I don't have to screw plates in and out of tripod mounts.
Buy:
Amazon