Should I Use Multi-Domains?

I haven't used this plugin before so I'm just trying to understand how it works....

I have a WPMU subdomain install on domain.com so every blog URL is: http://username.domain.com.

I also own domain2.com, domain3.com, etc. and I want users to be able to have http://username.domain2.com, http://username.domain3.com, etc. to display content different than http://username.domain.com (i.e. a different home page or different category of posts)...

Will this plugin allow for that?

Or does this plugin only allow toggling between all the domains, but the content (pages, posts) and even themes must remain the same?

Please clarify for me how this works. Thank you in advance!