Shelly's WiFi devices are all fairly cloud-optional - you can completely disconnect the internet and they will all work with Home Assistant just fine. Still, I'm not as excited about them as I used to be (mainly due to realizing there's a ton of cool-looking I/O flexibility they have that ends up being redundant once you settle on a control plane for wifi - MQTT in my case), and because their exposure of features and properties is somewhat inconsistent across device families.

But as a way to unburden your (usually one and only) Zigbee channel from certain types of chatty messaging, such as high-accuracy presence sending or complex lighting curve adjustments that can't be done ergonomically (or at all) via Zigbee, they are invaluable. Wifi (jailed in a VLAN, if you like) also provides a layer of failure protection should your Zigbee coordinator die unexpectedly.