It does not look to me that there is a lack of engagement in ZigBee when we talk about big companies. For example, Philips Hue and Ikea Tradfri product lines are constantly expanding and seem to work quite well. I have a few Hue products myself and I love them.
I am not into home automation, but it looks like ZigBee is popular with those users (see Zigbee2MQTT, ZHA, ioBroker). I would like to know, why do you think ZigBee projects are not “interesting”?
To answer your questions:
What’s it for?
You can use it to control a single device (lamp, fan, heater, door lock and so on), you can use it to monitor temperature or detect motion while being away. You can also control multiple devices and make them interact and build full home automation project, if you wish.
It will help if your electrical hardwiring is already completed and you need to upgrade/retrofit your system. For example, you need one extra light source or you want your wall switch to be moved to another place.
It will allow you to have portable devices (switches, sensors, plugs etc.) that you can easily control and program.
You do not have to be an advanced user to do all that.
Is the end useful?
It looks so. Why would so many devices be introduced if there was no interest. I have mentioned a few scenarios how to use it above.
Reliable and safe?
I guess one could say it is adequately good for what it is intended for. It does not have a military grade security, neither does KNX, but it is the most popular automation protocol for wired systems. It is even used in such large objects like Dubai’s international airport.
As home automation, can you live with it? Can your family?
I am not sure I understand what you are saying about GHI giving oxygen to ZigBee. ZigBee is already popular and widely used. There are no signs that it is dying (or not receiving oxygen ). I guess you have some inside information. I would surely be happy if GHI could make interaction with ZigBee devices easier. Let’s wait and see what GHI has to offer.
Btw, @Gus_Issa, here is a few more sensors to choose from.