Amazing, you're right! Fluctuations are normal for (online) dealers, but three times as much? It's a matter of supply and demand: they are probably difficult to deliver / from other suppliers.

Both are still available, but for the one with Zigbee you need a hub (M2 or G3 with camera). I use both and am happy with both. Pictured here is the Zigbee sensor, the one with Matter and Thread is thinner and longer.

The hub is required.

Yes - it works very well via Deconz and Homebridge

I have integrated them into home assistant via skyconnect. Don't use Apple products, so I don't know exactly. In any case, you will need a zigbee coordinator.

Yes there is a CR1632 battery installed in the larger part of the sensor, they usually last up to 2 years and then need to be replaced.

Yes, time-based is also possible directly in Apple Homekit or via the Xiaomi Home App (Aqara belongs to Xiaomi).

Very probably not. I have mounted an Aqara vibration sensor in the letterbox as a test; it should be comparably strong. As the crow flies, the distance to the next active node on the first floor is about 10m. In between is the letterbox itself, which is made of metal, a glass window behind the letterbox, the staircase and then the wall of the flat and a bit of ceiling and plastic because the receiver node is in a flush-mounted shaft. No connection. Maybe it would work if there was another node as close as possible to the outside wall, such as an Ikea Tradfri adapter plug. This could then transmit the signal.

No, unfortunately that does not work. Despite the same radio standard...

I tested it quickly: The magnet and sensor may be max. 1.5 cm apart for me so that the status is considered "closed". Apart means: product photo 1, distance max. 1.5cm. Everything over 1.5cm indicates the status "open". I.e. you could probably attach the sensor/magnet to the bottom of the window in such a way that they just do not touch when the window is tilted in order to still receive the "closed" status.

Although Philips HUE and Aqara use the Zigbee standard, the Aqara sensors are not recognised by the HUE Bridge. A good alternative to bring everything together is a ConBee 2 USB stick on a Rapsberry Pi. Other possibilities are explained by the user "larsxyz" in the following article: https://www.digitec.ch/de/producttype/showdiscussion/welcher-hub-gateway-am-besten-geeignet-xiaomi-aqara-hue-ikea-11467

Thank you very much for pointing this out. A correction request has just been sent.

Ok.