It's interesting to work alone on a big-ish project with no one telling you what to do and not having to explain anything to anyone. It easily feels ten-times more productive (in terms of accomplishment), but then again it won't have a business case and one doesn't get paid, either.

I think I'm least productive in open source (again, in terms of felt accomplishment), because if one isn't the sole maintainer (like above), then it's a pretty safe bet that few changes take less than a certain baseline (eg. 1 hour) -- someone always has a nitpick, CI always takes it's sweet time, oh, did we discuss yet in which branches we wanna merge this? Ah, please avoid puns in documentation and comments. Do we want this? Can you write this differently, like ...? Did you manually test this or that scenario ...?

(Now this also has advantages in terms of stability, quality and consistency -- but it's also obviously far, far less efficient)

On the clock it's more like "Meh, change that and that, otherwise it's good, so merge it after these changes and tell ops to put it in prod"