They can scam you and you domain might be deleted even without any notice. Refer to this thread - > https://forums.digitalpoint.com/threads/dot-tk-scam-me-again.2573013 Some free domain name provider "might" not allow you to point their free names to name servers. Once you develop it to be a good domain, they "might" ask you for a hefty amount to get it going. There are many other tensions related with free domain extensions. Go and buy a domain. it will be tension free and you can have a good control over it.
When i first started online i learned SEO and blogging by using a blogger.com free domain. Obiously there are other free domains you can get that are not subdomains. While they are good to learn with, if you want to make a living you need to buy real domains. Free domain disadvantages -Hard to rank for keywords -You can never sell the website -Somebody owns the domain not you (Landlord holds all the rights) -Nearly impossible to make a living with
I've had good luck ranking blogger blogs. Also some experience with co.cc domains which I occasionally have seen in the SERPs.