A start/stop button in a car is a little bit pointless without comfort access. Most cars you still have to put a key in a slot and turn it - or a fob into the slot and then push the start/stop button which requires more actions on your part than just turning a key.
With comfort access, the start/stop button makes total sense.
The ridges on the top of the door handle are for locking the car. There is another sensor on the inside face of the handle for un-locking. The range is very good from a security point of view. Even two feet away from the car and it won't unlock. So if you were standing at the front of the car no one could creep up and open the door and since the range is limited, no one can open the passenger door as you approach the driver's door. Also, your passenger can't lock the passenger door from outside even if you are standing next to the driver's door. Fairly clever system. And it is impossible to lock yourself out or leave the key in the boot.