IMHO, Workflowy stands up beautifully against the competition.
It has features available in no other outliners, with more being added each month ~ and, after reviewing countless apps over the years, I’ve found no equal for my own task management.
As for pricing, the app must charge enough for the business to be sustainable ~ and the free version provides just enough capacity for users to determine if they want to go all in for a paid account. This all seems quite reasonable to me. 