But relaying on those free domains which you don't know is a great risk. You can earn but what if owners take back the domains or cancel your account ? you will loose all your SERP and content. A total lost and you ll need to start all over again. For example Blogger don't like 100% affiliate blogs. If they find you have a blog filled with affiliate ads in every post then delete it giving you various reasons ( Being there) If you backup your content after each post at least you can salvage content and restore into your own Wordpress blog but you will loose all the backlinks and traffic you work so hard to get.
This is why I use these free domains or sub domains to make web 2.0 properties. That way you get full use of those free resources and also it won't hurt your earnings if you loose it.