I have quite a bit of experience with them.
I started years ago doing feral dog control with a German Drilling SxS 16ga over 9.3x72 it worked very good for what we used it for. It wasn't mine but the die was cast.
I had a Savage 24 223 over 2oga. The ergonomics sucked, you had to mount the scope too high to be able to get at the barrel selector or hammer. Sold it, but the idea was good in a 22Lr or something that didn't require a scop it would be fine.
A few years back I found a very nice V. Bernadelli 12ga over 5.6x50R Mag, two triggers(front triggera set trigger for the rifle) and tang safety. Very easy to operate. With the soderred ribs between the barrel it isn't a rig to shoot groups with unless you wait for the barrel to completely cool down between shots but it does put the first shot in the right place everytime. It has a fixed improved mod choke and shoots BB's well.
Bernadelli I have put lower rings on it since this pic.
Doing it's job
Right now I have an Fausti/Stefano combo gun imported by American Arms in the 80's in transit. It is a 12ga with choke tube over 222 Rem, with seperate barrels.
Will add pics in a few min.
Valmets, FinnClassics,Tikka, Savage 2400 are great rigs as are most of the Euro rigs. if you look hard there are a number of them out there that are fairly reasonable. The Bernadelli was $1100 because it was in a nearly impossible to get calliber, I handload everything using RWS brass, I only have a hundred rounds but they should last longer than me. The AA 12ga/222Rem was $600. Be wari of German guns with claw mounts , if they didbnt come with the gun they can cost close to a grand. Both mine have 11mm ribs on them so finding low rings is a little tough, but I did find a 11mm to weaver adaptor that only adds about .125" to the hight will be testing it the next couple of monts to see if they will hold up to the 12ga recoil.
To find them they are usualy grouped with the drillings on auction sights so just do your search for drillings and you will see the combo also.
The russian guns are heavy, nearly 8.5 without scope, but they feel stout. Bud's was runnig them at around $600 new.