If you canceal before 30days it wont charge you anything. If it worth? It depends how much you shop on amazon. For me it worths as i do some shopping and dont forget prime means free 2 day shipping and you get free prime videos and movies to watch on computer xbox ps or roku like amazon enabled media players.
Besides that if you use your student e-mail adress you can get student prime membership which i think 6 month free and $40 a year.