generally reccomend that everyone use an Aromatase inhibitor (AI) when using aromatic compounds... even just a very low dose (for those that are lean and low estrogen producers) is better than not at all. Letting estrogen levels run high (or in some cases rampant) is never good and increases a great number of health risks, not to mention the rather immeadiate effects on gynecomastia (which are ongoing... eg.. gyno was there, was growing, developing... long before you "noticed it".. usually an inflammatory or high hormone event will trigger an active phase-- ie "getting gyno".. but thats not really the case... that tissue was there being groomed and growed... by excess estrogen and other hormones)
with 250mg sustanon a week, need will generally be low... and you probably CAN go without... if lean and young.. and some people are such low aromatase producers that its basically a non issue... but for most people, even with low doses (or when natural for that matter) an Aromatase inhibitor (AI) (dosed to need) is generally beneficial.