I'm not going to write an academic paper here with all the details but the high level version is that I wrote software to send orders at identical times to both IB and TD and compare total costs. Sometimes TD was over $100 higher cost when spending just $5,000. These were trades for volatile equities with high trade volume at the time. You obviously won't see such big discrepancies when trading something like SPY. To do this right you need a trade size that is taking more than the lit liquidity at NBBO. Citadel and other PFOF firms basically get you because the SEC allows them to trade with you based on displayed bids/offers yet there is tons of dark liquidity at NASDAQ and the other large exchanges.
%% Good read but the headline photo conflicts with the news article ,so they should clean up those conflicts. All those fees are disclosed in any public broker. NO body works for nothing\ even ''non profits.'' Charity work maybe an exception. Maybe their lawyers advised against it; i wish they would have put some names on the 2 or 5 brokers.
I get great fills with fidelity, within .01 for virtually everything, for trades up to 500 shares, with no commish..... huge savings (I'd spent 33k on commishes in the 18 months prior to zero-commish pricing)
the biggest cost is the cost of being w r o n g try being right , it helps. see my posts for guidance
%% THERE is more than a few market makers; G1 Execution, GS, MS, Citadel, VIRT, JPM, Apex 2sigma, + Wolverine [+ BAC] is on some lists dont know why that list excluded them , maybe not as much business?? I dont even know the % Citadel has. I'm looking @ bigger trends + not order intent\cancels. Sure, as you noted , any market with fewer dealers or lower volume = wilder.