For those who need a primer, check out https://www.compareclosing.com/blog/all-about-mortgage-tranc...
https://www.npr.org/2014/04/01/297686724/on-a-rigged-wall-st...
PFOF and HFT mean that no matter how much you win, the exchanges and HFTs will always win more.
It's extremely hard to win as a small-money day trader, so I won't play that game.
Also, Citadel is buying retail order flow because they’re reasonably certain they can capture the spread and not get run over by an institutional trader with more information than the market maker. They aren’t frontrunning your 20 share order because you aren’t going to move the market by purchasing 20 shares.
Zero commissions and tight bid/ask spreads are better for an individual than no PFOF and $5/trade transaction fees with 25-50 bps bid/ask spreads.
https://www.kalzumeus.com/2019/6/26/how-brokerages-make-mone...
If you ignore all the transaction/processing fees. You could borrow some number less than your principal balance at today's rates ~5%, and use that to buy your current mortgage at a discount (it dropped in value). But your monthly payment would end up the same. Higher interest on a lower principal balance.
Roughly.
Even the worst of the liar loans didn't sell that low (the whole problem is nobody knew how to price them, but they were sure they were worth something).
Only bad debt is sold for such a discount. A normal mortgage with nothing wrong with it will be sold at full value, i.e. sold to someone who wants to make money on the interest.
A 100k loan today that pays back 105% a year from now isn't worth 100k.