Currently I use Time-estimate rollups and the biggest issue with that (a huge issue in fact) is that it still uses closed subtasks in the roll-up calculation, so if you've finished half the sub tasks, you don't see the time estimate of whats left and still have to work it out manually.

I can't understand why you'd want to include closed sub-tasks in a time estimate, but you could always add the option in the click app if you wanted to keep both options available to people.