They connect to your account using a service like Yodlee, Intuit Aggcat, or Plaid.io. So all they really have access to are your transactions. (I worked with these API's for over 1 year, and can spot that sign up flow a mile away)
They then pull in the transactions for you to round up manually (through a simple select process), and if you choose to round up, they ACH that amount of money over.
Makes sense for people who are not used to saving money or budgeting for financial services.
If you read The Lean Startup there are examples in there. I mentioned above WPEngine did it, but also look at Food on the Table. These stories show the lean startup done right. The story above is so riddled with holes. It's like the guys heard some buzzwords, read a wikipedia page, and ran with their limited understanding of it.
I would bet you'll be in the first (or second) roll out of fiberhoods. My best bet is UT Austin and downtown first, plus surrounding neighborhoods. Then they'll move West, then South.
They said the roll-out was focusing on Austin City Limits, and more specifically they stated the desire to release Fiber in public buildings (offices, hospitals, schools, etc.).
This paired with the UT Austin teacher video they released leads me to believe it'll be available to the campus area, probably downtown as well (St. Davids main and Brackenridge Medical Center) and probably the surrounding neighborhoods.
Personally, I would be surprised if it went east of I-35, south of Capitol of Texas highway, west of Mopac, or North of 183 in its initial release.