Just put in Linksys Velop 2 channel system (AC3600). Walmart ran a special for $150 for AC3600. Replaced a single AC instance. Wifi strong around whole home and outside.
If you have Sonoff devices and not tech savvy (likely if you have Sonoff you know what you are doing), be prepared for some reconfiguration.
Having a bit of trouble with port forwarding, ended up configuring bridge mode for now with AC router and radios turned off.. All traffic seems to get blocked by the Velop, even with port forward configured.
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Edit: Got Sonoff devices back in service. Just redid the sign on to eWeLink.
All in all, looks like this will be solid service for years at the house. Reality is about 20 minutes setup per node as firmware has to update and reboot. If you use port forwarding, DHCP reservations be ready for more time. If you are just a home user and want to improve WiFi coverage, seems to be a good product. If I remember, will post a 3 or 6 month follow up.
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Edit another follow up.
Port Forwarding worked as advertised out of the box. Never did determine why it failed initially.
Summary: Velop works fine and if you don't do anything special like port forwarding, reserve IP Addresses and similar setup will likely be about 20 minutes per node. (5 minutes is possible without a firmware update). This is a reasonable replacement for a single WiFi access point without having to think about the details. I wanted and got "Whole House" coverage. The garage works, the patio room works, the outdoors around the house works and no more slow spots in the house. Easy to turn on guest network. My Amazon Firesticks have come to life. Apple TV is snappy. There are now zero Ethernet wired devices except for the gateway Velop node to the cable modem.
My Broadband provider is Xfinity at 65Gbs capped at 1Tb / month. That is quite sufficient for just wife and and I. Speed test confirm the service via Velop.