The second part of the questionnaire is timed and the use of a smaller screen required you to shift from side to side yo completely view the answers. This additional time manipulating the questionnaire so you can read the answers can have the effect of lowering your scores. We, therefore, do not permit mobile devices.
It should also be noted that proceeding with a mobile device may result in your existing early or the page refreshing as you adjust screen size. The instructions warn you not to allow browser navigation or screen refresh since you cannot return to the questionnaire once you start.