I like the idea of being able to link todos to emails. You can categorize todos into into folders for different activities or projects. You can set reminders, due dates, add notes, and send emails with regard to the todos. It has its own calendar and you can export your todos to your iPad calendar.
Currently the app only handles gmail mail accounts. It would be nice if other email could be accessed. I would also like the ability to link todos to Contacts, but this is not available at this time.
I prefer this to-do manager over others I have tried mostly due tho ease of use.
GeoJr59 about Handle: GTD To-do List and Calendar Management