I downloaded it last night. The AR requires noticeable phone movement while it maps out the area to project on, so it's physically impossible to just pull your phone out and start cheating.
EDIT: the app specifically creates a 3d map of the local area by tracking changes as you move the phone. It requires gestures not entirely unlike the "wax on, wax off" movement from the Karate Kid. It's very noticable if someone tries to do that. It's possible that future iterations of the tech will not require that, but I don't see it as an issue at the moment.
Edited by PhantomFO