1/12" is going to be great for someone.
Round ball is 'bore rifle', sabot/slug is sabot/slug.
They're different.

The shallow, sharp rifling profile at 1/12 will have roundball stripping at high velocity.

For the guys who want to run solid 5/8oz copper bullets in sabots at 1500fps in their shotgun-only areas and seasons this little rig will be just the ticket.
The price looks nice too, and will likely get a few guys into their first double rifle. Good for them!

Peter-
I've been chasing work. It's quite a bitch out here around the bay right now, but I'll make it through - just need more of the day than usual to do it. I've only had a few moments to peek in here lately, fewer to write.
It's two in the morning and I'm just getting on here for a moment before I pass out and charge into another day!

Cheers
Tinker