Hi Justin,
You are correct, we don't have a true sprint burn down chart yet. As you mentioned, the Remaining Work Trend chart is close, but it is not constrained to a release or iteration. It's purpose is to show the trend of the work remaining on the sprint backlog items in the project. The iteration progress bar is basically a counter showing you how much time has passed in your iteration so far. For example, if it is 25% full, then 25% of your iteration has passed already.
We will consider adding burn down charts that work with the scrum template in the future, but cannot commit to anything at this time. Including a detailed description of the way each of the widgets functions would also be quite helpful. I have added both of items to our backlog.
We appreciate the feedback and if you have any other comments, questions, or suggestions, please let us know.
Regards,
Joel