The ARM is good when you know you will only be in the house for a short term, or you know your income will increase,  you should plan on refinancing to a fixed rate before the loan adjusts to a higher rate.

With a ARM you mortgage will adjust, this can put you at a disadvantage; you should look into refinancing into a fixed rate and term. That way you will not have the worries of; can I afford to pay my mortgage when my ARM adjusts. With a fixed rate mortgage you will always have the same payment the rate would never adjust.