I went to Metro today and the cashier at the self checkout was adamant that she didn't need to put in the PLU code. I think I might go back and redeem another ten just in case.
Edit: I just did a chat. They said the PLU code is to be input by the cashier but she has put a note on my file about what happened and said if I see the 50 air miles next week I'm fine. Also, this redemption is something you can do up to 4 times, limit of 1 a day so if you have enough miles it's a great deal!