well it is and isnt right now. Not all apps work for ART and will force close (whatsapp, capital one, and others). For me I have not run into any issues and I have noticed a difference when scrolling in apps. Hangouts doesnt lag at all when scrolling fast through conversations, same with instagram and g+. However each app will take up a little more space after switching to ART since they are compiled before hand now. For me, everything took up the same amount space when I was running davlik on 4.2.2 so i didnt mind at all. But if you keep davlik on 4.4 you will notice about 400 mb extra space.