I build all my projects, including a SQL lib, an EC2 interface, http and fastcgi frameworks, various web apps, and a mail merge system in notebooks, in nbdev and it’s made me much more productive.
Amongst folks that have used nbdev for 1+ years that I’ve spoken to, all report a 3+ multiple of improvement in productivity (based on non rigorous self assessment). This could however be biased because these people also report enjoying coding much more, so it’s possible some of that effect is the time just doesn’t seem as long.
Personally, after coding previously for over 20 years in various IDEs and editors (and for instance being prolific enough in vim I often gave talks about it) I wouldn’t ever want to go back to that old pre-notebooks time.
But it’s a huge investment and requires a lot of relearning - to get the most out of it you have to rethink just about everything. So it might be better for those earlier in their careers that haven’t got as many habits to change.