"21st Night attaches your notes and flashcards to the source you originally got them from"
This seems to be the main thing that might differentiate this program from Anki (other than the specially made decks for particular subjects, which could also be a big thing). This seems to be done, based on the demo deck, with tagging? This being an important differentiating factor, if possible it might be good if the example decks had more detailed contextual links rather than having just "from textbook" (without indicating which textbook) or "from life".
If there was a more clean explanation of the differences between your software and other similar products it might be helpful.
All my Anki note types have a field `HiddenNotes` which is never displayed on any cards. In addition to adding information when the card is created, I can also go back and add something to the field while reviewing in Ankidroid.
Try creating a note, then highlighting a phrase from that note. You'll see that you have the ability to create a card from that phrase, which will then be attached to that note. The next time you pull up that note, you'll be able to see the card and vice-versa.
You can also see attached cards and notes side-by-side if you prefer working that way.
This seems to be the main thing that might differentiate this program from Anki (other than the specially made decks for particular subjects, which could also be a big thing). This seems to be done, based on the demo deck, with tagging? This being an important differentiating factor, if possible it might be good if the example decks had more detailed contextual links rather than having just "from textbook" (without indicating which textbook) or "from life".
If there was a more clean explanation of the differences between your software and other similar products it might be helpful.