I love the TextExpander support in DayOne. Would love to see it in Agenda also. The TextExpander keyboard is not an option for me on iOS – too slow and clunky and breaks the workflow. Integrated support is the way to go.
DayOne has put a lot of effort into their own syncing solution, including end-to-end encryption. Yet they’re still confident in offering TextExpander support. Perhaps you could ask them about the security of TE support 