As to why it's better, elemental blast is random in which stat it gives you while UF is just a flat dmg increase. Potentially EB could come out on top if you are very lucky (multistrike buff on most of the casts) but on average it's weaker. You want to use EB on any fights with cleave because UF doesn't buff chain lightning, so on twins, brackenspore and tectus I run EB.
Yea sorry should have said it was for elemental. And how much dps loss is it to use EB in any other fights than cleave?
I just really love the visual for EB