Since I bought it, I've been using it connected to my computer via USB, but it never fully charges. Even when I unplug it and charge it separately with a wall adapter for 2–3 hours, it still won't reach a full charge. Most likely, the battery is already worn out.
I contacted customer service and sent them an email. Two days later, I received a vague response saying they would "see what they can do," and now it's been five days with no further reply.
With this kind of product quality and after-sales support, I think leaving a negative review is more than fair.