It's niche but also designed for more than a single person to use at any one time, and so you shouldn't think of the pricing as "per person" but rather "per team / group / family".

As an aside, what I'd find useful is an app that pipes together mine and my friends RTM or Todo.ly or Wunderlist to-do lists so that when I add a task it also updates their accounts (I assume this is possible with the RTM api).

Keep up the good work though. Have fun with it!