Think of the Epiphany as a special edition ION and the EOS as a special edition ION XE.
The Epiphany is an aluminum ION, to be short and simple. After the ION XE came out, which had a different feed neck and a bolt-out-the-back system, the EOS was released to be the revised Epiphany.
Ion is to epiphany as Ion XE is to EOS.
They all shoot good and the EOS is a good gun for what they sell for. I don't really care for the ION or the ION XE personally. The Epiphany was just a piece of crap for what you ended up paying for it. I don't necessarily suggest the EOS, I prefer the Vibe's to be honest, but there is nothing wrong with them and they shoot pretty good.