Thanks for sharing this little app, this is a wise idea and indeed, things are a bit easier with it!
However, it works only in one way: if the epub is correct, the message displayed is (for me):
"Epubcheck Version 3.0
Validating against EPUB version 2.0
No errors or warnings detected. "
But if there are errors, here is the message displayed:
"Version 3.0 Epubcheck
Validating against EPUB version 2.0"
This is to say: nothing!
The cmd window disappears too quickly for me to read the error message.
Two solutions perhaps: to prevent the cmd window from closing or copy the error message and redirect it into the text file.