So I use this in production at my company. It's an awesome tool. Personally when I'm coding in python I like to prototype in jupyter, copy code over, and then reimport anyway. Nbdev streamlines everything so I can write docs, tests, and code all in one place. And since the docs are just a jekyll site I can copy it to our documentation aws bucket in continuous integration. And with one command I can run all the notebook tests in CI as well.
The packaging is also really well thought out. I don't have to stress out about connecting setup.py with whatever publishing system we have. The settings.ini makes things sane and I can bump the version whenever I want.
A get a lot of skeptical looks when I say the source code is in notebooks, but that's just syntactic sugar for the raw source code. You still get to edit the raw code files and with one command sync everything with the notebooks. From my point of you it is close to a pareto improvement over traditional python library development.