The difference between 2.4GHz and 5GHz bands are speed, and reliability.

The 2.4 GHz band is the oldest, it has the ability to connect to your device from longer distances and all around be more reliable when it has to go through walls, ceilings, concrete, etc.

The 5 GHz band is the newer, faster cousin of the 2.4 GHz. It can bring blazing fast speeds within short distances, but the downfall is you need to be a lot closer to the Calix. It has a hard time going through materials like walls, ceilings, concrete, etc.