Deciding whether to use or trade the Mirror of Kalandra in Path of Exile depends on your goals, playstyle, and current in-game wealth.
The Mirror is an extraordinarily rare currency that creates a perfect, immutable duplicate of a rare (non-unique, non-corrupted) item. Because the mirrored copy cannot be further crafted or changed, it’s best reserved for items considered near-perfect or final version builds. Using a Mirror on a mediocre item wastes its value, given how difficult it is to obtain — similar to how spending poe 2 currency on low-impact upgrades can limit your long-term progression.
If you have a high-value item that you want to keep while effectively doubling your power or stash of that gear, using the Mirror makes great sense. This is especially true if the item enhances your build significantly and you plan on using both copies or selling one later for substantial currency. Mirroring allows you to preserve the original while getting the benefit of two items.
On the other hand, trading the Mirror itself is often the wiser choice if you do not have a truly top-tier, near-perfect item to duplicate. Because the Mirror commands hundreds or thousands of Divine Orbs in trading value, selling it can provide a large influx of currency that might help you improve your character more effectively through multiple smaller purchases or crafting attempts. This is a particularly practical approach for players who want to quickly advance their gear or those who do not yet possess items worthy of mirroring — much like players who buy poe 2 currency to jump-start their build in a fresh league.
Use your Mirror of Kalandra only if you have a rare item close to perfect that you want to duplicate for personal use or to sell the mirrored item at a high price. Otherwise, trade the Mirror on the market to gain substantial profit that can accelerate your overall progression. Given their rarity, what you do with a Mirror should be a well-considered strategic decision balancing immediate utility versus long-term wealth gain.