moose314

This is really what sold UBI for me. Making it possible for more people to give entrepreneurship a try and explore their business ideas seems like it could be very valuable to our society. I'm not saying it would be a slam-dunk great investment, but it would do a lot to address this inequality of risk-taking ability.

Its not really clear who you are arguing against, the GP mentioned large market orders, I simply made the point that most brokers have worse order routing than the HFT firms and Robinhood is probably not much worse than anything else out there. Using limit IOC orders is a tool that more savvy retail traders can use to prevent bad execution, but if they are trading size the commission they pay to the broker won't make much of a difference.

I would also point out that having your IOC order not fully filled is also bad execution. If you want to get a certain size done, repeatedly IOCing the market with manual click trades is not ideal.

The top of book liquidity on most equity stocks is light enough that a single retail investor can absolutely submit orders which must hit multiple exchanges, especially if they do so at non-peak hours. The NBBO doesn't help you if every market maker retreats before your broker can hit the next exchange.

There was a post on Reddit just a month ago where a small investment club did just that. https://imgur.com/gallery/qMBAzoQ

The other commenters answered your first question about the sale of flow to HFT firms.

Regarding your second question, I wouldn't recommend trading a lot of size on Robinhood, or using market order in general, but brokerages that charge commissions do not necessarily offer better execution than Robinhood, many of them still route your flow to an HFT firm or have less than stellar order routing systems.