Does it basically cancel out freight train? Does one activate then the other? Is it worth it?
I don't have good clarity on it. Also seems to be a lot of confusion in posts / comments on the subject.
Because of that, I went with a stack that was on one of my favorite RBs this year, the 94 Barry Sanders. He got first one free baked on, and then you could do a freight train X-Factor (which was the consensus best stack). He played great. So I've reversed it for Perry, since he has the baked on freight train. Been working well so far.
100% worth it if you do it right
Basically it will help the first juke/tackle interaction miss on a run or pass. Ideally you want to juke before you are engaged in a tackle. Then the next tackle attempt will be freight train kicking in for another broken tackle. Ideally you can win 2x interactions vs defenders if used properly.