I used to rebuild the Baikal SxS shotguns for cowboy action shooters, and ended up doing a few of the combo guns as well. As Bbj pointed out, the Remington Spartans are really just the same crappy Russian made Baikal guns, but imported by Remington instead of European American Armory, so they're relabeled. After that name change, they became even MORE popular among cowboy action shooters for a while until the whole deal took a dump.
The trigger can be improved, but a smith that isn't used to them can make them unsafe pretty easily. The trigger pull on most of them is about 300lbs out of the box and feel like you're dragging a sled over gravel, but a GOOD smith, familiar with their triggers can get them down under 6lbs pretty easily, but getting under 4lbs was kinda dicey.
A lot of smiths refused to work on them at the time, simply because you can't really get replacement parts for them without buying a parts gun. They're also not made of the finest materials, so it's easy to polish through hardening and ruin a part (and a few parts won't be hardened at all!).
The warning that I would offer is this - that second barrel is loaded and ready to go, and there are few things in life more exhilarating than having a double barrel slip fire on you and give you a delayed double boom when you're not ready for it.
The Savage combo guns are a much better investment if you're really interested in one.