As I said in the past, items that "set a stat at 18" aren't actually AS POWERFUL as some make them out to be. Which is why they are rated as "uncommon" even in the official material.
They are typically an useful early game crutch, but on the long run it becomes good enough just for secondary stats, as anyone will want to go above 18 on their primary one AND thse items don't stack with your base value or subsequent investments on the same stat.
This means that any wizard that will naturally aim to achieve 20 as natural value for INT will have no use for that type of headband, for instance.
It's another matter for a class that uses it as a secondary stat, like an Eldritch Knight.
And frankly 17 as a odd number makes this item considerably less appealing. For all intents and purposes 17 is pretty much as good as 16, outside of few fringe scenarios.
