Since the merge request on GitLab didn't work, here are two tiny patches for two minor improvements.
It was the optimization dialog presented at start-up that triggered me to make the changes. With the current text it is unclear what will happen when clicking the OK button. It's either nothing or optimization will be disabled completely (since there's a button for just DAVdroid as well).
I changed the text of the OpenTasks dialog with the second patch, since it's almost telling you you should have the app now.
Let me know what you think.