Like most firearm manuals their lawyers are heavily involved. Went online to Pedersoli's "muzzleloading guns owner's manual" and found the following for percussion doubles:
"With one hammer placed on half cock position and the other on a rest position (down), (NEVER PLACE BOTH HAMMERS AT HALF COCK POSITION AT THE SAME TIME), place the first cap; PLACE JUST ONE CAP AT A TIME, you can place the second one only after having fired the first barrel."
And for my double flintlock-
"When using the flintlock double barrel shotgun you must pay extra attention during shooting. Starting with the hypothesis that both barrels are loaded, ready to shoot, when firing the first barrel, the flame could also ignite the second barrel, setting the shot off. To avoid this risk, we recommend leaving the pan of the second lock unprimed, while firing the first barrel."
Following this advice makes skeet doubles somewhat problematic and pretty much defeats the purpose of a double gun.
For a flintlock bird gun, half cock is pretty much the only option as hammer down means an open frizzen and empty pan. I'm fine with carrying my flintlock at half cock. Same with half cock on a percussion gun.
Bottom line, utilize but never trust the safety on any gun. Don't be afraid to make the gun safe by uncapping/depriming in a dicey situation (bad footing, crossing fence, etc.) and control your muzzle. Pretty much the same as any bird gun. Otherwise, don't worry about it and enjoy the hunt.