Jacobi played Professor Yana for most of the episode, but played the Master for about five minutes after he opened the fob watch. Then he regenerated into John Simm's Master, who was seen for the further five minutes or so of the episode. That makes a fair comparison of which Master you preferred -- they each had five minutes of the episode to appear in.
And don't worry, you're not being attacked, you're not invisible and you are noticed.
