Local leafleting has a reply rate of about 1-2% but costs 200-300x as much to reach the same number of people, which means you only need a 0.005 response rate on Facebook to get the same value. A decent Facebook ad campaign will have a response rate around 0.08 - 0.1. That implies facebook advertising is 15-20x more effective than leafleting. Facebook ads might convert less well, but I doubt they convert 10x less well.
Local adverts on Facebook make sense, it's just a case of making them easier to use and selling local business on the idea.