WHAT IS THE GOAL?
Do you want to count visitors at a single location, or do you want to manage multiple locations? The scalability of the solution plays an important role in this question. Likewise, possible future expansions should be considered in advance. So perhaps at the beginning it is enough to simply count the inputs and outputs. But perhaps in the future, people will want more intelligence, such as, filtering employees, or integrating with other systems. Then you are well advised to use an expandable system.