I've decided to give Art another try. I'm still not convinced it's MUCH faster like being claimed here... But how could it be? It might be a teeny bit quicker but that's it. Not complaining, although whether it's really worth half a Gb of storage on an already fairly limited storage capacity is another question. Can't really comment on the battery as yet.

I enabled ART on my Moto E, which with hindsight was a bit silly as it gulped up about 0.5GB - and there's not a lot of room to begin with.

But on a slow(er) device it has to be better to have compiled data in advance? Arguably the difference will be least beneficial on a Snapdragon 800 device or faster, as the JIT method is going to be quick.