I immediately noticed when I switched brokers how much better the prices were, even on limit orders. When I used Robinhood I was 19 years old with no way to know better, aka their dream client
For a buy scenario. If a stock is trading at $20, other brokerages would execute a market order at $19.9997/share where Robinhood would execute a market order at $20.09/share. I noticed this also would occur but less noticeable on limit orders