Effect
Spectator selects or names any card - true free choice, no forcing.
You then take your phone, go to photo gallery and show that last picture in your gallery is picture of playing card they named - proving that you knew which card they will name.
Effect is not limited only to playing cards, but I think this is best use of it.
Skill level
Principle is not difficult to understand, but you will have to spend some time practicing.
I practiced more that 30 minutes to be confident to show the trick to my wife :)
I would practice even more before showing the trick to complete stranger.
Tutorial
Text tutorial is built in the app and is easy to follow and understand.
Settings
There are some setting you can make but I can not share this because I would reveal too much about the principle.
I can at least share that you can set up the password you have to enter in order to launch the app so nobody else will be able to launch it - might be important to somebody.
Summary
Very nice effect and good app.
Only negatives I see is that graphical design of the app is not very attractive which however does not influence the function.
I believe that when you launch the app, phone screen should look like its turned off - this works OK on devices with physical buttons, but on my phone without physical buttons I can still see Android navigation buttons. I believe this could be improved in next release.
I was also not able to do immediate reset.
To sum up - good app, few minor negatives. I can recommend it.
Score: 75%
