The difference is like night and day. The amount of keyword suggestions they provide can not be matched by the free service. I also think their paid data base is updated more often then their free database is. If you are going to use it for multiple accounts it will be a great time saver. but if your using it just for your own domain then you can get away with the free one no problem. it will take more work and more input from the users side but it can be done for free.