It's like there's an echo in here. Or merely consensus. I think the killer app for the Dual Drive was Euro city bikes that people used to commute in business clothes, because it could offer a reasonably effective chainguard. That wasn't the case with Bike Friday, who made a lot of NWTs with DD, even though they already had an effective triple crank setup (prior to wide doubles); Might have been for the higher-high than a lower-low, or issues with a long-cage rear derailleur 25 years ago. But yeah, I avoid DDs due to the more complex maintenance and not having the facility to do so myself. I wouldn't turn down a Rohloff 14, the drain and fill lube sounds quite straightforward. For now, I'm infinitely happier with my 2X 405% versus my previous 1X 273%. Doesn't sound like a lot of difference, but it is.

Thanks for your other info, that may be useful if go lower than my 30T low cog.