Because of it size it is easy to carry in a bag when on a train.
It has 4 lights that are green when fully charged and it has a on/off switch which is good. You can turn it off to save power which last for a long time until you need it. Turn on and use cable, to use to charge your phone. When you get the Samsung battery charger you also get in the box 2 cables for mobile phone and tablets. This meets my needs and very happy.