Unless you want e-mail or web browsing capabilities or go on the current $15 plan, there's no logical reason to choose Public Mobile over Chatr.
Public Mobile's other voice plans just don't cut it. Before Public Mobile started offering web browsing, there was no reason to sign up. After adding applicable add-ons such as Canadian long distance, Public Mobile's voice services would come out to the same price as Chatr, Wind, or Mobilicity which is the most likely reason Public Mobile has so few customers. Wind and Mobilicity got customers over Chtar because they offered data and had agressive promotions on plans that included data for the same price or less than Chatr was charging for plans without data. Other customers signed up to Wind or Mobilicity for plans that included limited time discounts or prepayment discount on voice-only plans. Public Mobile's plan offerings were a complete failure for the longest time.