I agree with you regarding mountain duck.
For Boxcryptor and file stream, they work fine but with minor issue which I submitted before. the encrypted placeholders are double of bytes larger than the actual file. this is corrected as soon as the file is cached locally however, it will miss your day if you are using any synchronizing software. for me I synchronize a certain folder with an external hdd. if the software checks the file size it will overwrite the file.