I know this because I wrote an app that connects to Alpaca accounts (as well as other brokerages) to help people build their own custom index funds [0]. It only took a few weeks to build our Alpaca integration, whereas other brokerages often take months/years just to get access to their APIs.
You specify pies of funds with weights.
They automatically allocate funds and dividends to the underweight entries, and have 1 click for rebalancing.
It's not made for single-real time trading, there's one trading window each day.
Sure beats the spreadsheet and whole-share issues when I did it for free with Robinhood.
I feel like their UX priorities are screwed up big time. But as a platform, they're my favorite as far as concept/functionality.
https://www.cnbc.com/2019/04/18/a-controversial-part-of-robi...
Now robin hood _did_ get fined for "not perform[ing] systematic best execution reviews of several order types". If that's what you were referring to then fine. But if your complaint is just about selling order flow you should better understand what that means. Maybe start with patio11's How Brokerages Make Money[0].
[0]: https://www.kalzumeus.com/2019/6/26/how-brokerages-make-mone...
They list several ways in which they "will" make money. My (possibly unkind) reading is that currently they're burning investor money.