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.net. When I click on one of the links instead of it being their domain name sometimes its www.whatever.cjb.net and it can get really confusing.
So, for less confusion and more professionalism would choose a paid domain name.