With no money at the door, every chip you win is upside and every chip you lose costs nothing but time. That is genuinely different from a paid tournament, and it changes the game in two directions.
For you, it removes the risk-of-ruin question entirely. There is no downswing to survive and no stake to protect, so the only resource being spent is hours.
For everyone else, it removes the discipline. A player who paid nothing has no reason to fold, and a large part of the field will treat the early levels as a coin-flipping contest. That is not a flaw in the format — it is the format's defining feature, and it is where your edge comes from.
The trap is treating "free" as "valuable by definition". Five hours for a shot at a share of a small pool can be worse use of your time than one hour at a micro-stakes table. Free is not the same as profitable per hour.