Just got given a free £5 voucher for picking up the reservation I had made with Argos.
They have this offer currently to promote their new store opening in Westfield Stratford.
No sure when the offere finishes but guessing will last until the end of the weekend.
So if you are that area and buying something from there just use your smartphone to make the reservation online and pick up your goods as normal and get your free £5 voucher.
Hope this helps someone.