The four big differences between this new second edition and the previous first edition Hieratikhon Vol. 1 are: 1. the size of the book/font, 2. updating to STM/SVS Psalter text, 3. Layout tweaks, and 4. Printing issues. We clergy are very picky about any changes because of how frequently we are "in" the books, but I am a big believer in constructive feedback so I will offer my opinions.
1. I prefer the older size that is more pocketable, but as I age I am sure I will start to appreciate the larger text. My suggestion for the eventual third edition is that you do both a "pocket sized" and a "large print" in the same size as the Dimtrikon. You'll sell both and there will be less quibbling. Everyone wins.
2. Translation changes are very polarizing and should be minimized in my opinion, but I think it was wise to move from RSV texts we have to pay the NCC to use even though that is my preferred translation. This new STM/SVS translation could use a tweak or two down the road, but it's good enough and if our end result is a complete liturgical "bible" in a reverent understandable English text that we don't have pay others to use—that is worth our current generations being in "the messy middle" so we can hand our kids and grandkids a unified American Orthodox English translation for the services and scriptures.
3. New layout options I've noticed (moving the menologion so the more-frequently used parts aren't at the beginning where they wear the spine out more quickly, streamlining Cheesefare week) are improvements. I'm a bit bummed that one of the ribbons changed color, but that's just me being particular.
4. The black over red printing annoys me, but it may not annoy you. One of our newer members donated two of these second editions to our church and we are thankful to have them, but I will continue to use my pocket-sized first edition until it is too worn out.
I am thankful for STM for (finally) making these available again and putting up with us nitpicky priests who have very strong opinions about these books. May God bless your good work!