One thing to keep in mind; "IF" everything goes as planned any safety method is unneeded. The "Fly in the Ointment" is that unexpected things do occur. What happens if you trip on an unseen vine or step on a rock that rolls & in either case lose your balance & fall. That open gun may well close in the process & those hammers are still cocked. Additionally the gun, especially in the hinge area is much more likely to be damaged in a severe fall when open than when locked shut. many older hammer guns did not have efficient check hooks either & depended on the forend iron butting against the bottom of the frame to stop their opening. this can put tremendous strain on the bottom rib via the forend lug. I have one Pieper hammer double with a loose lower rib most likely from this very cause. Carry them "Shut" & Bolted & hammers in the safety notch. Rebounding locks are generally safer than non-rebounding ones but with care those can also be carried wuith a reasonable degree of safety. In spite of many old wives tales hammerless guns are actually safer to carry about than hammered ones.
