For anyone looking for room/area-based BLE detection, the Bermuda integration (disclosure: I wrote it and have all the biases) works with Shelly Plus devices (and esphome proxies) and gives fast responses to area changes and home/away status.
I don’t have any Shelly’s myself (yet) but others are using it successfully. The Shelly’s do seem to have some limitations on how much broadcast traffic they’re willing to send (looks like they cache 3 seconds worth as of v1.0) but if you’ve multiple devices in an area that would probably even out OK.
It updates every second, as long as the proxies have sent new data.
It has support for Private BLE Device and iBeacons, so you can get iOS and Android devices working in it, too.
I’m interested in giving better support to those who are trying to use Shelly devices so any input on how to optimise the advert forwarding is welcome - although a lot of it seems to be well-covered in this thread already, so I might point people here for specific help.
Community thread: Bermuda - Bluetooth/BLE Room Presence and tracking [custom integration]
Github: GitHub - agittins/bermuda: Bermuda Bluetooth/BLE Triangulation / Trilateration for HomeAssistant