This is NOT a single line reefing system. The clew reef lines are independent of the tack attachment. (I use a hook on the Cunningham to tension the tack.) What this is is a convenient way to run the clew lines forward inside the boom to the mast (and back to the cockpit if you choose) so they don't droop down externally.

An upside down bullseye mounted just inside the forward end of the boom facilitates a smooth exit for the internal reef clew lines.