I suspect it may have an always on option. But the spec for the battery test says it includes 90 time checks so we can assume it will turn off.
"How reliable is it at realising you want to know what time it is?". I guess it depends on the user.
For those who are not used to wear a watch it will probably work fine, because they will learn to use the gestures for switching it on.
On the other hand, for those who are used to a standard watch and know that there are lots of different gestures you use to see what time it is - some that doesn't even move the hand but just shifts the glance slightly- it is going to be totally inadequate and disqualify it as watch.