Since speed was never really a problem with this phone, ART has little to no benefit, it takes up about a gig or so and has poor compatibility with many apps. From my testing, around a quarter of my apps fc, blinkfeed was maybe a tad smoother, the rest of the system was already butter smooth, so far, not worth the trouble, not to mention it breaks xposed, in the future it may be worth looking into as theoretically it is better than dalkvik.
ART is definitely smoother and snappier than dalvik. Apps load much faster because they are precompiled. Should be few issues if any. I have personally tested over 75 apps, all worked fine.
Sent from my HTC One using xda app-developers app
Can you go back and forth between Art and Dalvik with no issues?
CC