Does it really clean the air without a filter?

It releases negative ions that make particles clump and fall out of the air. That is different from a HEPA filter, which traps particles. Expect less effect than a filter unit, especially in a large or dusty room.

How big a room does one unit cover?

The maker rates it for up to 250 square feet per unit. That is a small bedroom or office. Larger or open rooms would need more units or a fan-driven purifier.

Does it make any noise?

No. There is no fan, so it runs silently. The trade-off is that it does not circulate air, which is why its effect is gradual.

What comes in the box?

The purifier, a wall adapter and a USB cable. It can also run from a laptop, car port or power bank over USB.

Is it safe to leave running overnight?

It is ETL and CARB certified, and ionizers of this kind are commonly run continuously. Some people are sensitive to the static or faint smell ionizers can produce, so try it in a room you use before relying on it overnight.

How does it compare with a HEPA purifier?

A HEPA purifier pulls air through a filter and traps particles, and it usually has a fan you can hear. This unit is silent and filter-free but does not trap particles or move air, so it is a lighter-duty option.