I've successfully used the previous version of the edit conflict tool quite a few times, however the new version completely failed.
First, it took me uncomfortably long to find and grab a copy of the text I was trying to add. Perhaps it's just because I was seeing the new version for the first time, but it was an unpleasant start.
Next, I was severely puzzled that there was no live edit-box anywhere. I after a bit of effort I did manage to activate the old-text as an edit area and add my own text. I am going to be cautious in commenting because it's my first time seeing the new version, but I have a vague but strong feeling that that this design is very wrong somehow. It's hard to give more specific feedback because the system-as-a-whole failed completely.
After modifying the old-text-area to include my new comment, my natural next steps would be (1) preview and (2) a diff-check, prior to saving. Except the preview button didn't work! Repeated clicks on Preview did nothing. I was unable to get to diff either.
Unable to progress, I went back and tried to review and absorb the conflict-system as a whole, and see if maybe I was missing something. I can pretty much see what you were aiming for, but when I tried the system for expanding/collapsing sections(?) it was either broken or not doing what I expected. I couldn't find any way to get the preview button to work. Somehow the whole design around activating the edit areas felt very wrong.
I was never able to resolve the edit conflict. If I can't go back to the previous version of the tool, I'll have to shut off the Beta-preferences and go back to the "native" conflict resolution system.
This may be a strange comment, but I get this weird feeling that new design went wrong because someone from the VisualEditor or Flow team showed up to take charge.