I live outside the US ... A few extra pounds...
Make yourself a favor, buy an arduino DUE (~ $12).
I have been using esp8266 boards for some time and have found very few compatibility issues with libraries and sketches. The libraries and sketches that don't work usually rely on CPU registers and instructions that are unique to the ATmega series of chips. Often, they are not even compatible with the entire ATmega range, just the atmega328 and atmega1280. These libraries and sketches won't be compatible with samd21/Zero either. Over time, they will either be updated, if they are valuable, or abandoned. But sketches and libraries that don't rely on features unique to ATmega chips generally run absolutely fine on esp, samd21, stm32 etc.There are lots of us Brits on the forum. Yes, some US items can seem less good value for the money, especially with the value of Sterling at the moment. Have you tried Pimoroni, Pi Hut, HobbyTronics?
Looks like Adafruit have just released their new SAMD51 based Arduino Mega style "Metro M4 Grand Central" board: https://www.adafruit.com/product/4064.
I have created an Arduino board for myself. 480MHz clock speed, 1MB SRAM 2MB FLASH. With some stuff already on board (like 6 servo connectors) STMH7 uC used
Nice! How did you do that? Like how did you get the bootloader working? Can you share the details of your project please?
https://www.pjrc.com/store/teensy40.htmlTeensy 4.0 features an ARM Cortex-M7 processor at 600 MHz, with a NXP iMXRT1062 chip, the fastest microcontroller available today.