Personally, I think its one of the best in the game. So I decided to take a look at how hitters fared against it through the month of April. Below is the chart:

The thing that I note is there are a lot of swinging strikes and foul balls very near the bottom of the zone and just below the bottom of the zone. His change has nice tumble to it and it drops off the table at times. Of the 14 balls put in play against his change up in April, 6 of them went for hits. That is a higher number than you would expect actually. By looking at the chart, it seems that a lot of his strikes actually are coming on balls outside the zone. The quick fix would be to not swing at the pitch as often, but given how deceptive it actually is, if you guessed wrong and its his fastball, its not going to drop off the bottom of the zone and you now just looked at a strike.