My daily commuter is a 40-45 year old Gazelle with an SA3 and rod brakes. I've ridden it for more than a year but the only problems I had with it were with the much newer parts like battery fed led lights. Modern Gazelles or Batavus' aren't build like that anymore, Azors are.

It's about 24 kilo's and that's not ideal in the mountains but it doesn't feel heavy to me. Efficiency is about so many other things, big steel wheels that want to keep rolling help maintain a steady pace, the head tube angle helps to keep a straight line, the upright posture makes you use your strongest muscles and helps not waisting energy with upper body movement, the diamond frame doesn't flex much, the SA3 has pretty low mechanical drag and and there's no dirt on the chain or a derailleur to cause friction either.

In the 10-25 km/h range for a non sweat commute on flat or mostly flat terrain it doesn't get much better.