Both of these settings allow you to have more control over the devices connected to your network, with slight differences.
Allow Internet Access
When "allow internet access" is disabled, customers can connect to the current Wi-Fi network but cannot access the internet. This feature is useful if you want to disable a device momentarily, such as your child's tablet, or an old laptop you don't use much. The device won't have internet access but it can easily be turned back on when desired.
Block from Network
When a device is blocked from the internet, this device cannot connect to the current Wi-Fi network, and the device cannot access the internet. This feature is ideal when you notice an unknown device on your network, for security reasons it is always wise to block any unknown devices so they cannon access your network.