Many thought the same thing about TouchID. We will all need to use it ourselves so we can form real world opinions.
For example the OP mentioned a bunch of scenarios where I just use "Hey Siri".
Driving, "Hey Siri read messages", "Hey Siri Call xxxx", "Hey Siri give me directions to....." etc etc.
In the office, there are times that "Hey Siri" maybe inappropriate however in those situations you "generally" want to look at your phone anyway. And if you are raising your phone to see it, it can see you.
On the nightstand. Again use "Hey Siri" or if you want to see something on the screen it will see you.
I'm being bit of an apologist because I was critical of TouchID and they proved me wrong. So I'll give them the benefit of the doubt this time....at least until I use it and prove them wrong.