Hello Hirias,
Is there a reason you say, “if you must use due dates…”? Is there a reason to favour deferring an item than having it Due by a date?
Also, I notice I made a mistake in my original explanation. The “Due again” and “Defer until” behaviour works as I would expect. If I have it set to 1 week, for instance, then it will be due or deferred 1 weeks AFTER I click Complete.
What doesn’t work well for me, and doesn’t make any functional sense to me, is that the way “Repeat every…” option is handled. It doesn’t move the next due date into the future if the last due date was more than the selected timeframe in the past. Meaning… If I click DONE on an event that was due a month ago, and it is set to Repeat Every Friday, then it will be next due on a Friday three weeks in the past. Then two weeks, then one week, and then this week, and only then will clicking DONE make it due NEXT Friday.