PFOF - could be big or could be nothing. https://www.reuters.com/article/us-brokerage-kickbacks-idUSKCN1AV1KW
Routing is so complicated that it will probably take years for the regulators if they are dedicated enough. For one thing, it's impossible to define what is best routing nowadays.
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.
Call it what you want - it's a fact. The news is a buzz with this very thing, the DOJ is investigating this. Fidelity does provide direct trading to some of the ECN's, not the IEX which is a good work-around if you can sit in front of your monitor when you want to enter/exit. Fidelity sent 34 percent of its orders to Citadel Securities and 32 percent to KCG. https://www.cnbc.com/2017/08/15/mas...ng-top-u-s-brokers-for-kickback-conflict.html https://www.bloomberg.com/quicktake/payment-for-order-flow