I have a Belkin WiFi Router which offers a feature of a secondary Guest Access WiFi network. Of course, the idea is that the Guest network doesn't have access to the computers/devices on the main network.

I also have a Comcast-issues Cable Modem/Router device with mutliple wired ports, but no WiFi-capabilities. I prefer to only run one router/DHCP/NAT instead of both the Comcast Router and the Belkin Router, so I can disable the Routing functions of the Belkin and allow the Comcast Router to

But if I disable the Routing functions of the Belkin device, the Guest WiFi network is still available. Is this configuration just as secure as when the Belkin acts as a Router?

I guess the question comes down to this:

Do Guest WiFi's provide security by 1) only allowing requests to IPs found in-front of the device, or do they work by 2) disallowing requests to IPs on the same subnet?

1) Would mean that Guest WiFi on an access point provides no benefit 2) Would mean that the Guest WiFi functionality can work even if the device is just an access point.

Or maybe something else entirely?