I am sorry to sound condescending but if you read my post, a rather short one, I said:
"and mentions it as some kind of "responsible disclosure" towards end."
Arbitrage money is net of fees between exchanges so your ELIF showing $5 profit is kind of irresponsible giving people false information. If you are concerned about your users do mention the fees in bold letters above fold.
On your question on exchanges in US, well read this:
And I mentioned NBBO because it nearly removes arbitrage opportunity not because there are only "two exchanges". But if you want to change your goalpost to focus on M&A, I digress.
Arbitrage money is net of fees between exchanges so your ELIF showing $5 profit is kind of irresponsible giving people false information. If you are concerned about your users do mention the fees in bold letters above fold.
On your question on exchanges in US, well read this:
https://www.investopedia.com/ask/answers/08/security-market-...
And it doesn't even mention IEX:
https://en.m.wikipedia.org/wiki/IEX
So no not only two exchanges in existence.
And I mentioned NBBO because it nearly removes arbitrage opportunity not because there are only "two exchanges". But if you want to change your goalpost to focus on M&A, I digress.