How much accurate is free Keyword Research Tool?

Smith is right, in addition to that always use more then one source and in my experience free sources will never be as good as some paid sources. Many paid sources are just there to save you a lot of time, all of it could be done for free but it would take MUCH longer. I would go for a good paid software like market samurai, and cross reference with other tools like google keyword tool, google trends, etc...