Bought this app because the price of about five euros seemed to me a warranty for a well-developed app. But the first version was complicated and with many errors. The new version for iOS 11 has a better look and lay-out and should work in almost every app. But on my iPad the app made two errors from within Mail: not only the encrypted message is sent, but also the not-encrypted original; the mail reaches the adressee with first a lot of lines with only the character D and finally misses the last lines with signature.
The app changes to Shift position even if you only try to correct a typing error.
