I did it earlier on today. I opted to use the code on which it was a simple touch screen. Then it opened the door which opened quite wide so it was obvious which one was yours. It was chest height as mine was a small package (would have fitted through a letterbox) I suspect had it been bigger it would have been higher or lower. I got it pretty quickly so dont know if there's an time limit on getting the parcel ie it shuts after 3 minutes.
Overall it was a quick and easy process so I will probably use it again if I know that I am going to the supermarket that week rather than make a special journey. I had more trouble with the self service checkouts in the supermarket than the Amazon locker lol.