Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Frustration

When these pens work they are amazing, however, the refills are very bad. They may write beautifully for up to a month, but, although it looks like there is still plenty of ink in the cartridge, the pen will no longer write. It has come to the point where I test them before I buy them at the store and if they fail to deliver, I return them. This is a real problem buying through mail order, but I do love the Ion when it works.