What may thrill one person may not thrill the other. Hence, you have to study each person separately to know their individual needs.
Having said that, and based on my personal experience, the reason why I joined SFI is:
* It is FREE to join because I don't to put my hard earn money on something someone just introduced me to.
*Again the FREE TRAINING resources that will be available. I want to learn and know what I will be spending my time and money on.
There so many things that can convince someone to join SFI but these two attracted me the most because those are my needs.
BUT if you are doing an advert for people you don't know at all, it is good you list as many reasons as possible so you can cut across almost everyone's need.