I actually signed up for that same exact program last night! From my research, it seems to be very legitimate, and the fact that they have been around for a long time is also a very good thing. Unfortunatley, I dont think that I will be using this program that much, because I saw that you have to refer other people, and I absolutely suck at doing that. If you know a good way of getting referrals you should do just fine with the program. I hope everything works out okay for you, keep us posted on what happens!
SFI is a legitimate program. I've been with them for about a year now and I really can't complain. I haven't made six figures yet, but that's because I haven't put in the required effort. With SFI you reap what you sow. It needs time and real dedication which is pretty hard to do if you have other jobs. If it's all you are doing, then you are likely to strike gold.