Interesting alternative 32-bit GRBL controller using a Teensy 4.1. Super Gerbil boards were never in stock, so this might be an alternative solution for 3+ (5) axis control and 7 relay outputs.
Teensy 4.1 - https://www.pjrc.com/store/teensy41.html
grblHAL Breakout Board - https://www.tindie.com/products/philba/grblhal-breakout-board-unkit-for-teensy-41/
@RichCournoyer, a possible solution for your Super Gerbil woes?