TCURDT  There is a command line tool called nrg2iso. But it's quite old. Not sure it will still work with new images. Heard rumors that you can just rename a toast file to iso and that is supposed to be enough. But I never tried that ...and frankly speaking I doubt it will work - at least in all cases.  
(Version 1.1.2)

TCURDT  Unfortunately they keep changing the format. So for newer files you might have to blame MagicISO. It's a cat and mouse game.  
(Version 1.0.7)

TCURDT  Please have a look at the screencast on how to use it.

http://vafer.org/projects/uif2iso4mac/

(Click on it to get the bigger version)

It works from every standard print dialog (Apple+p). Which also means it works with all printable documents.

But yeah ...I will provide a README with the next release.

Thanks for the suggestion.  
(Version 1.0)

TCURDT  Could you please be more specific? What did not work for you?  
(Version 1.0)