You really don't need to install third-party plugins for this.
Just create template override for com_users registration and there you can hide username field and copy email field value into this field on form submit.
so this is gone be pure Joomla solution,
do it like this:
- go to http://katalog.dev/administrator/index.php?option=com_templates&view=templates
- open template needed
- "Create override" tab => com_users => registration
Now you have override. Next step is code changes
- See changes needed to files here at gist.github (you need changes from "alex7r revised this gist")
Note that file name is not com_users_registration_default.php
but com_users/registration/default.php
. And full path is /templates/YOUR_TEMPLATE/html/com_users/registration/default.php