in irl matches like gen con, i do not recall any injunction against something like this. it is a crutch for memory for his own mage, not info on his opponent for example. it does not give him any special insight beyond a reminder text. i can understand your viewpoint however. because, there is no guarantee that his note is just for himself. i could contain insights on his opponent, tendencies etc. however since this is online, such notes could easilly be handwritten next to him and you would not know. not sure how it can be prevented here.
come to think of it, in a irl match, something like that is easier to catch as a judge. perhaps grizzly can chime in as he has been a head judge for several tournaments.