Product review (4 stars): Great for what it is!
For size comparison, it's about the size of a soft ball. The top simply twists off revealing the water reservoir. It is simple and basic plastic, but it works well considering you are working or sitting near it. It's not by any means a home humidifier for a large spaces, so if you are looking for a diffuser for an entire room this probably is not for you. I think the main plug being USB is a giveaway that you will most likely need to sit near it to get the most from it. I would also recommend using distilled water because as the water diffuses it can leave minerals behind clogging the system, greatly reducing life and making more cleaning of the product. For what it is, it works well.