That little metal ring next to the CL is possibly the best place to attach your leash (what the bottom right arrow is pointing to in Tom's pic).
It's what Best recommends and what I do. What it does is depower the kite as much as possible when you release to it.

I am personally wary of attaching to a rear OS. I have had too many bad things happen with that. That's just my opinion though, and I know many riders trust that rear OS. I don't. I would rather take my chances with the depower ring and if getting dragged in the water 'cuz it didn't fully depower, just let the kite go (QR the leash). My reasoning is that the depower ring usually puts the kite in the water (if released in high winds). If the kite is still moderately powered and I am getting dragged, at least it's not looping. I will have time most likely (and not be getting looped around) to QR my leash.
The rear OS has the possibility (however slim) of pulling a death spiral on you. I have been in it and seen them happen. I don't understand the physics of it (seems impossible) but I don't have to, I have seen it.
In those scenarios, you might be surprised the ride you would take. Up and down in the water.. changing speeds and directions.... it can be hard to reach your leash QR (I think Bill proved this recently)
So, I might be a tad paranoid, but you literally couldn't pay me to leash to a rear OS for fear of the death spiral.

If you are planning on ever attaching to the rear OS on the Best bar, undo the velcro associated with them before you start riding. Those velcro things when attached make the rear OS inoperable (useless). If you don't undo it and then QR to a rear OS... plan on getting royally screwed (I am not exaggerating).