More efficient? It should be the opposite: two compressors should be more efficient than one. Yes, smaller compressors are a little less efficient than bigger

More efficient? It should be the opposite: two compressors should be more efficient than one. Yes, smaller compressors are a little less efficient than bigger ones, however unless you always open both the fridge and freezer doors, it's more efficient to cool them separately. The big downside to dual compressors is cost and complexity.