In addition to this, I would have an external 1-4TB usb HDD as an additional backup, in case of power surge, malware etc that could wipe out everything on either computer, no matter how many drives you have in it. It's cheap and you can do an entire HDD image using macrium or "win7 legacy backup" built into win10 & make recovery disc while you're at it, to recover from windows being unbootable etc.
RAID 1 protects against drive failure, but if the data you're mirroring is deleted, corrupted, or encrypted by ransomware that will also be mirrored and you'll wish you had an external backup. Wherever you set it to save the image, don't rename 'win10backup' folder it puts them all in by default, but can rename the folders within it. Even if it's just once a week, running backup to this drive on a set day so it's easy to remember. More convenient to set it to autobackup, but if you leave external HDD plugged in it's vulnerable to malware/power-surge.
A simple hack to protect against malware/ransomware is to make an image backup on a small partition you don't save anything else to, then delete it. Ransomware should miss it, but it's easy to recover as long as nothing's written over it. For this, add another 1TB HDD to desktop if you don't want to keep plugging in an external, it'll double as a backup HDD you can quickly swap to replace the 1TB you're mirroring the M.2 drives to if it fails, without having to wait until a new one arrives.