I have tried Slim in 6. And I loved it!!!! I did lose 30 pounds with it, and sensible eating, of course. BUt I didn't keep up with it, so here I am. I actually want to get back into because the workouts are pretty intense and after completing one, it just makes you feel better about yourself.
It has 3 sections:
Start it up - you are supposed to do this one until you feel comfortable with it (I would do this one for about a week, because after you get it, it really isn't that challenging.
Ramp it up- definitely more intense. you should stick with this one for about 1-2 weeks. this workout is a killer!!
Burn it up - the name says it all. you are supposed to do this one for the remaining time left of the six weeks. this one is really intense and it'll kick your butt.
I bought mine 2003, so I don't know if there have been upgrades. Mine came with the resistance bands and those are awesome. My bf even uses those to workout.
The only bad thing I have heard about SI6 is it is pretty repetetive and there is a chance that you'll get bored and lose interest. I didnt lose interest thought, because I loved seeing the results. And the results are all worth it.