We haven't looked at NNEX files, so can't comment directly. However we do offer limited support for direct Evernote import.
The best approach is to export individual Evernote notebooks into separate .enex files, and then import each folder to CleverNote using the Import button on the web page.
We say "limited support" because Evernote offers a myriad of different note options, not all of which have a corresponding representation in CleverNote. Our view has always been that we want to focus on notes in the purest sense and not try to become a general purpose repository for all forms of media. This makes perfect sense when CleverNote is viewed as a front-end to Google Drive.
Hope this help. If you get any problems importing an ENEX file, ping us at
sup...@clevernote.co and we'll try to help.
/Joy