What incentives do mainstream brokerages have to building public APIs? It seems to me data asymmetry is the name of the game in Wall Street and it’s no different for retail brokers.
Are you actually doing this for a production app with income you rely on? Because Heroku has horrendous uptime these days. Lot's of random emergencies on both worker and web dynos. Don't forget you share routing with thousands of other apps too so expect random hiccups there too. It's easy to give this advice but does not scale well with complexity.