Unless you know the device isn't rooted this doesn't really achieve very much. On a rooted device an "attacker" could have replaced the crede tial storage with something that will conveniently store the data unprotected.
It is helpful as a way of ensuring random applications don't get hold of the data, but not for keeping the data from a determined user.
It is helpful as a way of ensuring random applications don't get hold of the data, but not for keeping the data from a determined user.