If they had been advertising about how low their fees are, and how you can invest your savings in ETFs or something I would have no problem with it since that is a reasonable thing to do. But suggesting that the average low income person should be day trading is just predatory.
I even saw an ad (not 100% sure if it was Robinhood but a similar product) that was telling a story about how someone was in tens of thousands of dollars in debt, and day traded until they were out of debt. All these trading apps seem to be targeted at people who will almost certainly lose money, and who generally don't have much to lose. I mean I have no problem with an app advertising an easy way to do day trading, just don't act as if it is anything other than gambling.