Lot’s of reasons for selecting the XIAO SAMD21 M0 board.
No need for the Wifi or BLE implementation, lower speed and as seen with the ESP32 libraries - more libraries - fewer conflicts provided you don’t need the wireless communication or higher CPU speeds.
It’s also much easier to solder directly onto a board as a “part” e.g. no parts or chips underneath.
I’ve used them as a programmable controller in power supply blocks.
I also use them on test jigs for other boards that I’m working on… need for wifi or a BLE implementation on a test jig controller.