@mandpw 

Hi, you don't have to disconnect the Comcast modem router. Since the default mode of Deco is a router and when they are connected together, you might have two routers.

It is very likely that you might have a double NAT issue. Thus you could consider configuring Deco M5 into access point mode:

• How to set up Deco to work in Access Point mode?

  @mandpw 

It could be simply explained as having two or more routers on a network and each router has its own DHCP and firewall.

Then devices that are connected to different routers are unable to access each other.

The following link would provide more details:

https://support.google.com/googlenest/answer/6277579

  @mandpw 
if I opt for the access point configuration what Deco benefits will I lose?

The following link would provide more details:

• What’s the difference between Access Point mode and Router mode on the Deco?

I have a Wi-Fi extender that I will be replacing. Is access point Deco like merely having multiple extenders or is it something better?

The "Wi-Fi extender" here, do you mean the satellite Deco M5 or actually a wireless range extender, like RE450?

if it is the satellite Deco M5, the overall mesh performance, like the speed of the satellite nodes will be better than normal range extenders.