Two things get said about the simulator, usually within a minute of each other: that it is a crystal ball, and that it is a toy. It is neither, and the gap between those two accusations is roughly where it actually sits.
What goes in
Your shape, your eleven, and a real fixture. From the opponent side it takes how that team has actually played — where they build, where they press, what they have given up to sides set up like yours.
What comes out
A scoreline, the chances the match turned on, and the part people skip past: where your shape leaked. That last one is the only bit I would defend as genuinely useful. A single scoreline means very little. "Your right side was two-on-one against nine times" means quite a lot.
What it is not
It is not a prediction of Saturday. Run the same eleven twice and you will get different scorelines, which is not a bug — it is the honest answer, because football does that too. Anyone selling you a single confident number about a football match is selling you something.
Everyone runs the same engine, so when two people in a room disagree, they are disagreeing about the shape rather than about whose version of the maths is kinder. That was the point.