I have dove with both the Delta 4 (my previous reg) and the EOS (my current reg). My diving is pretty varied, from lots of instruction in moderately shallow water to much deeper dives, but mostly colder water and even ice diving this winter. Both regs are incredible regs and when I replaced my Delta 4 with the EOS, I had no nervousness about passing my Delta 4 on to my 14 yo daughter. In fact, my wife now dives with the Hollis 212 / DC 1 which is a very similar second stage (if not the same) with Hollis' DC 1 first stage. I have no hesitation in recommending the Delta 4 and if you have the extra cash, the EOS is that much better. I used more than a few regulators too, and I have never felt the comfort and confidence of the Oceanic regs - with the others, there's always been 'one thing I would change' or 'one thing I don't like'.
In another post, Doug alluded that the Delta 4.1 is cosmetic change (brushed metal to black impact plastic ring) + no swivel. I personally love the swivel, the reg does not pull or twist when I'm demostating skills like equipment re & re underwater to my students. I am waiting patiently for Oceanic and/or Hollis to release the swivel as an accessory so I can add it to my wife's 212.
