There are -- especially big looping curve balls. I think that is part of what they have been adjusting in testing. Pitchers will surely try to exploit the edges of the zone. Of course they already do this and hitters are forced to swing given the inconsistency of umpires calling the corners of the zone. I would hypothesize that anyone with above-average command of the strike zone will benefit from this system -- but if the rules are as they are currently written, then hitters/pitchers will have to conserve their challenges and will not want to risk challenging borderline pitches in low-leverage situations.
So the tennis-style system will correct all of the obvious blown calls. Plus pretty much every borderline strikeout/walk call in high-leverage situations will get challenged, especially late in the game.
I haven't seen it mentioned, but I suspect there will also be a cheating element to deal with. Hitters/pitchers have to make the decision to challenge almost immediately with no help from the dugout, but anyone watching the game has immediate knowledge of whether it was a ball or strike. There are often TVs right behind home plate in the premium seating that will probably have to be put on a 10 second delay, otherwise the fans will yell out "CHALLENGE IT!". Or maybe the fans will try to trick the opposition into making spurious challenges. So much food for thought!