We recommend that you use the Real Exam Mode exclusively on your laptop or desktop computer.
It is possible to use a tablet or phone in this mode -- but it is not recommended because you want to prepare in the as most exam-like fashion as possible. And that means sitting at a desk, using an external computer monitor, keyboard, and mouse. Using a tablet or phone means that you are not practicing for the real exam.
This is why the simulator displays a warning message whenever you start the Real Exam Mode on a tablet or phone. This message is intended to remind you to prepare only under the most ideal conditions.
You will be able to use the simulator on your preferred device but you are reminded to use a "real" computer for full exams. (The warning message is not displayed in the other two exam modes.)