They arent really useful thing Actually Its not a valid TLD but just url redirection service. You can get free .co.cc domain, look at my signature
free domain are useless. Paid domain just cost around 5 to 10$. I have experieced all free and paid domains. Even i have experience with free hosting and paid hosting. Thats i am better to tell you my views.
there is .info for about $2 if you shop about and .eu for $4 ish i think Last i looked .com came in at $6 ish These free subdomains do have their places, but yes if you want to secure your websites life id cough up the money