A smooth bore slug barrel is no different inside than any other improved cylinder shot gun barrel of the same length.
The longer the barrel, the longer your sight radius, just like any other gun barrel. I doubt you will shoot enough slugs through it in a life time to notice a difference between a 24 inch barrel and the same barrel 20 inches, when shooting slugs through them both.
It is the adjustable rifle style sites attached directly to the barrel that makes a slug barrel a better choice for shooting slugs. Yet I've seen receiver scope mounts be perfectly satisfactory, AND I've seen a lot of wounded deer run on over the hill due to shooting slugs from from guns sworn to be "just as good", "very accurate", "never shoot very far".
I'm not sure what you've got but I think if it is something like this link, it would probably be pretty sweet. For Foster slugs use a modified to what ever MORE open choke you've got to shoot slugs. If you want to max out the accuracy for longer shots with a barrel like this one in the link, the replace the choke with a rifled choke and use sabot slugs.
Like anything else it often pays good dividends to try a few different brands but from what I've shot, mostly from Remington guns, I'd try some Winchesters first.
From my own testing, I would NOT shoot slugs through a full choke or tighter barrel. It will soon be a modified choke in short order.