Gravity Forms Better User Activation gives you control of the User Registration activation page. Choose any page on your site, edit it, and users land there when they activate their accounts.

Edit the activation content, including error messages, in the WordPress post editor. Four activation views cover success, an already active user, a missing key and errors. Over a dozen merge tags, such as {gpbua:username} and {gpbua:login}, fill in the details without links or code. You can also redirect users to a different page after a successful activation. Developers can use a custom page template, and page builder users can insert the content with the [gpbua] merge tag.

It integrates with Gravity Forms Auto Login, part of the Gravity Perks suite, to log users in after they activate.