The app contains a complete database of what is orbiting the earth. It allows you to find what is overhead, then view the spacecraft from earth, from above the earth, or right next to the orbiting satellite with the sun's lighting at the correct orientation. You can easily find what is above you at any time, and try to locate it with binoculars or with the naked eye if the satellite is bright enough. The satellite positions are updated every second, and the position calculations are updated every day.
This app packs a lot of power into an iOS device. It's just the thing to have when you are sitting out on our increasingly pleasant spring evenings seeing if you can spot some of the man-made traffic zipping by over our heads. My tests of the app were positive. No crashes, no surprises. Sometimes the animation could be a little jumpy. Lots going on in the background, but I never found it a problem. The app did everything I asked it to do, and worked quickly.
Even better, Satellite Safari is the official app of the Sky Cube Mission, which is expected to launch and deploy from the International Space Station in September. When it does, you'll actually be able to request your own images from/of Earth, and even 'broadcast' your own messages from orbit as 'tweets from space.'