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First Wi-Fi + Bluetooth HAT for Raspberry Pi with 40 pins at an affordable price, get rid of your wires, here comes the IoT HAT by RedBear
Very well done! And that's coming from someone with a competing project: https://hackaday.io/project/8678-rpi-wifi . Using a chipset that already has support in the PI's kernel is far more convenient than an externally built module like the ESP8266.
Nice choice on using the TI inverted-F antenna. It's a great fit for these kind of boards. However you may want to either scoot it more towards the center of the board as metal standoffs may interfere with the radiation pattern. Or consider extending the end of the board to put it outside of the HAT stack-up like my ESP-HAT design: https://hackaday.io/project/8678/gallery#5e2c5a3634aae88c96d96006b7dd9910