I used to use .cjb.net when I first learned how to make websites, My personal opinion on them is that their a hassle and buying a domain name is better than using the free types. They can be really confusing when you try to click on a link. I can't really explain it but the domain name like follows you or something.
Hmm how do I explain it,
lets say you have a website, and a links section...your website is www.whatever.cjb.ne t. When I click on one of the links instead of it being their domain name sometimes its www.whatever.cjb.ne t and it can get really confusing.
So, for less confusion and more professionalism would choose a paid domain name.