The foot itself doesn't worry me. It's the anchor that does.
I know they say the PD anchor connectors are rated to 200lbs, but they make me nervous. I don't mind using them on little point & shoot cameras or other light loads, but I don't think I could trust it on my 600f4. Even if they are capable of handling that much weight, the connector cords are so thin... it wouldn't take much to start wearing through it. And unlike a wide nylon strap that would show wear and fraying a lot more obviously, a thin cord might wear and snap long before it was easily noticed.
I opted for a QD port connector on a BlackRapid strap that attaches to the foot. Then I made my own safety strap from some nylon, a QD connector, and a locking carabiner. I sewed one side closed, then used a sliding buckle to allow for adjustment on the other side. I hook the safety strap into the QD port on my L-bracket on my camera body. The carabiner gets clipped onto the main strap. So if one fails, the other will still hold with minimal drop. I am all about redundancy.
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