Does it depend on style of trading? maybe i am wrong as i am just a week in SIM DAS trading and thinking of IBRKR
------<300K traders who predominantly places market orders(removing liquidity, thus ECN fees) and DOES NOT scale in/out(most of time) are better off by fix pricing as they will save big on ECN fees.
----<300K traders who predominantly places limit orders(AKA adding liquidity) does not have to worry much about ECN fees BUT ,for Scales in/out, have to make judgement call regarding how frequently or how much to scale in/out as they may have to pay $1 for all trades