It makes the point, but is unrealistic. Some of the camera views aren't broad enough and don't give viewers enough of the flight path of the ball to make a correct call. The "expert" setting is much easier than the "hard" setting just because of the camera angle.
I only missed one out of all of them and it was on the player challenged serve....(with the sound on)
just for fun I did it again with no sound and got 15/20 so sometimes I wonder...since you rely on the noise of the ball being struck while looking at the line if the crowd gets loud you lose some time looking for the ball comming.
then again I doubt lines men don't follow the ball during play - maybe during the serve is the only time you just focus on the lines?