You may get this alert when you try to open a file in the Finder after setting uFocus (or any other app) as the default app via File > Open With > Other…, then select uFocus and enable the option Always Open With.

This may be (according to an Apple engineer on the Developer Forums) a security feature, and is not specific to uFocus.

To open the file anyway, open the System Settings, select the Privacy & Security tab, scroll down and click Open Anyway.