I used the Outlook Add-In for a few years. I never was comfortable with creating projects in it and looked for something else.

I tried MLO and thought it was an improvement. But I ended up sticking with something called Achieve Planner by Effexis Software. There is a significant learning curve getting up to speed. Nonetheless, I am pleased with my decision.

When I used the Outlook Add-In, I avoided creating projects because the Add-In made it cumbersome. Once I started using a hierarchical outliner, I enjoyed creating new projects because it became so easy.

David Allen tells us to create a project if there is more than one NA. There is no chance in hell that I am going to create a project for 2 NAs unless my system makes it very easy to create one. If I avoid creating a project, then I am missing out on one of the great benefits of GTD: answering the question, "What is the desired outcome?" Now that it's fun to create projects, I am envisioning my desired outcomes all the time.

But, as they say, YMMV. As Merlin's podcasts demonstrate, David Allen does not believe that it is worth the effort to maintain NAs under Projects in an outline. I can only say that my experience has been that the migration from Outlook Add-In to a hierarchical outliner significantly increased the effectiveness and completeness of my system. I've been using this system for a year and I love it. I never could say that about Outlook, with or without the Add-In.