Laurona is an off brand Spanish import that frequently had double/single triggers. I have two, but they are both over/unders. Mine are set by recoil, and when I had the action reblacked on one the gunsmith who took it apart said they were not overly complicated, or difficult to work with.
I honestly don't know why that setup isn't more popular. Just grab the trigger for the choke you want first and pull again for the second barrel.
CHAZ
For no particular reason here is a picture of one of the guns in question. A set with 20 gauge and 12 gauge barrels on the same frame.
