"The inclusion of soft-metal "blow-out" safety at base of breach ..."
I have never heard of such a thing. It would be a suicide item. That rifle would be dangerous to shoot.
"...probably indicates quality manufacture"
Quite the contrary IMOH: To my eyes that looks like pure Khyber Pass production - genuine muzzle-loading barrel, maybe originally flintlock, no, sorry, - note how the barrel becomes WIDER in front of the backsight, and has a band in a position where no-one would put such a thing, as it would weaken the barrel. But not to worry, the bands look to me as if they have been faked up and are not real inlay bands, which always have clean, straight edges.
So TWO shorter barrels joined end-to-end and hammered into submission as a percussion rifle and brewed up with whatever fragments of other rifles were lying around. Please note that it was offered as a wallhanger, not a shooter.
Ermm, I presume that was intended as a joke?