HomeKit products work directly with your iOS device or Apple TV. Triggers and timers need one of these devices to be in range. Obviously and Apple TV works best as it's always there, but you could use an iPad in the same way.
So yes, to use timers, triggers and so on, you do need to use something as a hub. But you don't need a hub if you are present. The Apple TV is the best hub option because you get so many other features too.
Because the Apple TV is connected to the internet, you'll also gain remote access and control of your devices and sensors. So you can check if you left the back door open, or turn on the heating before you get home.
It doesn't work with Amazon Echo or any other smart home platforms but it does work with all Apple HomeKit enabled devices (all HomeKit devices with work with all other HomeKit devices). The reason you can't connect to other platforms is for security. Nothing's unhackable, but Apple HomeKit is the most secure smart home platform out there.
Date published: 2017-10-13