Although the quality of the rib will be the same as the original Winchester, the only way a Simmons rib looks OK on a Model 12 is if they DON'T put their silly name down the side of the rib.
There are some Simmons marked rib on Model 12s that were considered to be factory. So some look OK. The big problem is counterfeiting.
Side Story: I have a 1968/72 Deluxe L.C. Smith, one of 188 made. They were all fitted with a steel Simmons marked rib, and so stated in the Marlin catalogs at the time. So the marked ribs were factory for this model and look OK.