A live app demo is not the same as an introduction of what your app does. Getting the technology to work, logging in as a dummy user, creating some dummy files, showing some dummy output, changing some settings, quickly going back to the management console, before switching to the user screen. All this shows that the app is real, it exists, the beautiful design, the fast response time, the powerful algorithms. But it is step 2 in the introduction, the audience is missing step 1, the overall context of what problem the app solves, and what it actually does. Time to throw in some good old slides that can get these messages across faster/better than a live demo. Then, fire up the tablet.