Not only one, but one across ALL TYPES.
Saving a trials memento till you craft a weapon you wanna use in trials? Well too bad, so long as its in your inventory you cannot acquire grandmaster or gambit mementos! How fun!
Not true at all lol I had both trials and grandmaster ones in my inventory when they dropped you can have all types just one of each really stupid but get it right
Good to know, but in that case the description for the items is really unclear.
Says you can only hold one memento at any given time, not just one of each type.