This app worked like a charm.
We needed 100 discount codes generated so we could create gift certificates. The apps auto generated codes were too complicated so we created our own and imported them. Five minutes later all the codes had been created in Shopify. We exported the codes (to ensure they were correct) and printed our own gift certificates with a code on each cert.
It was a little labor intensive because we created our own codes and gift certificate but the results were well worth it. I would give the app and Shopify 5 stars if I could print the certificates directly from either place.