The thing Raphael used is called a power scanner, a version that can be used in combat.
This thing is rare not because the crafting method or the patterns on the lens are lost but because it requires a lot of rare materials.
It's made from many types of special, hard mineral rocks, plus a lens from a type of natural crystal with extraordinary durability. Only those with great strength can use those materials to craft it.
In terms of value, it's far inferior to storage crystals because it lacks practical application. Seeing the enemy's actual combat power isn't that meaningful, and at too high a level, it's not durable enough to withstand attacks.
The top powerhouses on the continent can already gauge relatively well whether an enemy's combat power is weaker or stronger than theirs. The margin of error isn't small, but in a fight like that, it's enough.
