@sjoe80 

Hey

Most home grade devices, the Deco included come as one SSID banded over both the frequencies, in practical terms there is no real benefit separating the bands as Band Steering is pretty mature now and will work for you.

In general band steering will force 5ghz capable clients to the 5ghz automatically and it's not really required to have a separate 2.4 / 5ghz setup in most use cases, use one SSID on both frequencies for convenience and let the Deco do the working out in the background as to which band each devices required..  Personally I would just leave the main SSID with both frequencies enabled and let it work away.

However if you want to make your IOT devices more secure, then by all means activate and use them on the Guest SSID, leaving the main deco SSID for your laptops / phones etc. 

The one main difference between the Main SSID and the Guest SSID is access control rules, namely anything on the guest cannot see any other device, it can only access the internet.   This is great for IOT devices like Plugs, Sensors, Alexa etc that really only need internet access and can help security.     Anything on the Main SSID can see other devices (not guest devices).

Hopefully that makes sense and helps!