PHILIPP M.  Thank you for your comment and your interest in Renamer.

We're currently working on a new help system and will release it shortly.

Regarding the bugs: please could you send us the details of the problems you're experiencing? We're committed to fixing any errors but please do let us know about them!  
(Version 4.0)

PHILIPP M.  Did you try this:

1. Drag in your zip files

2. Add a "Find & Replace" renamer

3. From the gear action menu select "Suffix only"

3. In Find enter "zip" and in Replace your new file extension

4. Click Apply

?  
(Version 4.0)

PHILIPP M.  Thank you HUBBERBUBMAN for your comment -- iArchiver now also handles encypted archives. It can create encrypted Zip and 7zip archives, and it can open encrypted Zip, RAR and 7zip archives.  
(Version 1.3.5)

PHILIPP M.  Devon: thank you for your comments and suggestions.

The modify feature is high on our todo list and will be implemented in the coming weeks.

Regarding the website: indeed the create DMG feature was somewhat understated -- following your suggestions we made this more prominent (http://iarchiver.com).  
(Version 1.1.2)