I used OpenAI's function calling (via Langchain's https://python.langchain.com/v0.1/docs/modules/model_io/chat... API).
Some of the challenges I had:
1. poor recall for some fields, even with a wide variety of input document formats
2. needing to experiment with the json schema (particularly field descriptions) to get the best info out, and ignore superfluous information
3. for each long document, deciding whether to send the whole document in the context, or only the most relevant chunks (using traditional text search and semantic vector search)
4. poor quality OCR
From the demo video, it seems like your main innovation is allowing a non-technical user to do #2 in an iterative fashion. Have I understood correctly?