How is this different from a plastic diffuser?

The body is glass rather than plastic, so it looks more like decor and feels heavier. It works the same way: you add water and essential oil and it releases scent.

Does it need essential oil to work?

Yes. It diffuses essential oils you add yourself; it does not come with a scent built in.

Glass wipes clean but shows water marks and oil film, so plan on regular wiping. Handle it carefully because glass chips and cracks more easily than plastic.

Where should I put it?

Any flat surface in the room you want scented, such as a nightstand, shelf or side table. Keep it away from edges and out of reach of children and pets.

It is a reasonable gift for someone into home fragrance, since the glass look makes it presentable. Check that they already use essential oils, or the diffuser has nothing to diffuse.