Yup Esters are the difference. E - long lasting A- Short. So with A you need to do more frequent injections (EOD,ED) and with E you can pin twice a week. Benefits of A are if you are new to Tren and you don't like the sides you can get off and the drug will be out of your system much quicker. Ive also heard some people saying with the more frequent injections their sides tend to be a little milder.