SpeedyBee BT Nano 3

This inexpensive (10 USD) but nifty little device lets you connect to the SpeedyBee app to configure Betaflight on your flight controller... via Bluetooth! All you need is a spare UART! I find this useful for builds that use an AIO flight controller that is oriented in a way where the USB is difficult to access and enclosed frames like some Cinewhoops. It's a lifesaver if you ever break a USB port on a flight controller. I make sure I set a spare UART to Serial RX on all my flight controllers beforehand and if the worse case scenario happens, I can just solder one of these on and access Betaflight with minimal drama!