Unless I’m missing something, both OmniFocus and Things capture tasks from Apple’s Reminders, moving them from Reminders to their app’s data, and then deleting the Reminders’ task(s) albeit via slightly different processes, Neither maintain a sync; a task either remains in Reminders or is moved.
It is the primary reason why I don’t use either app.
What I love about BusyCal and Agenda is their 2-way integration with Apple’s Calendar and Reminders, making it easier for me to share date between those two apps, and also with other Mac/iOS people who may not own Agenda or BusyCal, but certainly own Apple’s Reminders and Calendar.
Looking forward to Agenda collabortaion…