I had a brief conversation with the late outdoor writer Gene Hill at the Iowa Governor's Pheasant Hunt many years ago. I grew up carrying a single shot .410, so I was well aware of the issues involved in trying to cock just one hammer as you mount your gun on a flushing bird. Gene suggested carrying the gun broken open, loaded, and with the hammers cocked. As someone suggested above, that might work hunting preserve birds with pointing dogs, where you can walk trails and wait until the dog locks up. You could probably get by waiting until the dog points before cocking the gun. But serious problems arise when hunting wild birds--grouse and woodcock likely the worst cases--if you try carrying your gun open, loaded, with hammers cocked. You're quite likely to get crud from the cover into places that will keep the gun from functioning when the birds flush.
That being said, I did kill a double on sharptails on a windy day in North Dakota when my shorthair went on point. I was not very confident that they'd hold, and I cocked the gun (a vintage 16ga Husqvarna) as I walked in. They held and it all worked perfectly. But most of the birds I hunt most of the time don't live in short grass cover as do prairie grouse. Like Ted, I decided that while they're interesting firearms, I'll stick with doubles that have a conventional top tang safety and wait until the bird is in the air, taking the safety off after it has flushed.
