I think it's a fair point that some people can't actually craft the gun they have in mind right away.
As a returning player who went Flawless... I can craft a handful of guns, but most of them probably aren't that great, and overall the system is something I'm not very familiar with.
That encourages me to hold onto the item rather than use it impulsively.
But it'll be a waste if I don't use it before I go Flawless again.
Then, maybe I won't go Flawless again. I hope I do, though.
I just hope I find a use for this Memento before then.