We have used wristbands for 9 years now at the high school level, kids started to not understand hand signs something simple such as touches to the box (touches to chest and stomach). We use own the Zone and for some reason we might miss 2 signs all year. We use the same cards on offense, we have a new card for each game, we use it by never calling the same number twice, it works as we want to hit and run, there are 20 sets of three number sequence that work for hit and run such as 345 the players look down see two letters such as SQ and it tells them its a hit and run. We don't yell numbers and I will even go as far as to say it will take a below average coach and make him better as he now has to think about scenarios before they happen and if a pitch is a ball or strike and the count and possible count and who is on and who is on deck and what the defensive team does and who the pitcher is and how he is throwing. Its not complicated and players get it. We also have quick signs body indicators for times where our numbers dont mean anything or we dont want to give numbers, they are a single touch to the body, such as a nonchalant touch to the nose could be steal.
We use Nuemann wrist bands but the own the zone software and like I said 9 years of using it and yes I learned about it from college coaches. Who use it for offense, pitching and defensive scenarios.