NKit only produces GCZ files

Posted by User100 on .
If I extract the nkit.iso files from here, most of the time NKit generates the proper ISO file, but in some cases I only get a GCZ file. Why is that, and what can I do about it? (e.g. Just Dance 3 & 4 for Wii: https://vimm.net/vault/17628, https://vimm.net/vault/17629)