I made a quick plugin per request of @Veldaren
The plugin will select parts that are duplicates of other parts that have the same CFrame, and the Same Size.
It will ignore any descendant of the Camera, and will ignore the Terrain Object, so that other plugins in studio that utilize the Camera Directory do not suffer problems from this plugin.
Checks for similarities in: Size, CFrame, (If both parts are Unions) TriangleCount.
Here’s a link if you’re interested: https://www.roblox.com/library/589761793/Select-Duplicates-Plugin
EDIT: Use Case: If you need to optimize your maps and have duplicates you cannot immediately find this will find them.