I've never used my extinguisher and the arrow is in the green. Is it still good?

That depends...on a lot of things.  While the gauge being in the green is a basic indicator of the life of the extinguisher, age, location, type of extinguisher, and many other factors dictate if your extinguisher will work in an emergency.

It is always better to be safe than sorry, so it is best to have a fire protection specialist provide a free safety inspection and analysis to let you know exactly the situation with your extinguishers.