I have 4 Xiaomi motion sensors and also a number of their door contacts and two hubs.
Generally they work very well with HomeAssist (I have Hass.io running on a Pi3). The motion detection is instant but they do have a built in 2 min filter - meaning it won't detect more motion in the two minutes after initial detection.
Their detection range is 7m which works fine for most of my rooms.
The only problem I picked up was that they pick up my cats, so I aimed them a bit higher or put them deeper into shelves.
For the price and size (they're tiny!) they can't be beat.
Still need to block my Xiaomi gateways from phoning back home to China.
I also used one door contact as a transmitter for an outside PIR (Takex wireless). This works just as well and there's no delay. What's even nicer is that you can run both the Xiaomi door contact and the Takex PIR from 3v so they can theoretically share a battery and give the Xiaomi much longer battery life.
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