Consider getting a cable and a U lock as human error is the most common reason for a heavy lock to fail. Believe you might either not lock it, or lock the bike to itself. I would say 1 in 500 or 1000 locking attempts you will screw up with one of the locks. Also note the thing you lock to might be compromised. In NYC there have been thefts where bike rakes that were bolted to the ground (from above using friction bolts) where knocked over and the bike taken.