Since I can’t browse the live web or see which specific article you’re referring to, here’s what you should check to make sure the article is reliable and the firmware is safe:
If the SD card is for mining hardware (a common use case for specialized firmware), platforms like Zeus Mining host specialized "flash card packages". The Download and Flashing Process mxtronics sd card firmware download top
Do not use random file-sharing sites. Many "top" search results are fake or malware. Since I can’t browse the live web or
: Common for older or budget SD and USB drives. mxtronics sd card firmware download top
Only use URLs containing mxtronics.com or mxtronics.net . If the official site is down, contact support via LinkedIn or their official AliExpress store.