Just keep in mind they're pretty slow to cast in my experience. Echo just kills things so fast, that by the time they cast, they used it on mobs a screen away, and if you miss one, i don't think they recast until the bind wears off, or you resummon it.
I liked them the most on Apocalypse build, since the skill take time to cast anyways, they have plenty of time to bind to monsters you're about to attack. They didn't seem to do much after i swapped to Echo from my own experience.
When i was playing blood boil in p1 i was zooming around very fast and they were awesome. I had to be very fast or i wouldn't get mana from the hex since the monsters killed by defilers don't give you life/mana back.