This is not a ToS issue as the application will not physically let you do both on the same account. You cannot fly and control using the same account at the same time even on different devices.
However, if you have two separate accounts (different apple IDs, etc) you can fly and control on separate devices. Or even fly two different flights at once. In the eyes of the system, it is two distinct profiles.
While it is physically possible, it is frowned upon because you are not giving your full attention to one of them at a time. If you are controlling a busy airport it is not fair to the pilots under your control that you may be delaying responses because you are busy landing your plane on another device. Imagine if you were a pilot waiting to take off and were delayed because the controller was busy flying their plane.