PFOF - could be big or could be nothing.
https://www.reuters.com/article/us-brokerage-kickbacks-idUSKCN1AV1KW
https://www.reuters.com/article/us-brokerage-kickbacks-idUSKCN1AV1KW
I call b.s.I put an order the other day on my 401k at Fidelity. A limit order to sell a position at a profit target. The order showed it was at Citadel - the enemy. The orders are supposed to be in the brokers in-house servers until the order price or condition is triggered. Lost any trust in that broker - showing my hand to the enemy, unforgivable. Halted my trading in that account.