Mass grave uses the exact same method as a real Windows validation would. To MS it’s undetectable and if you register your hardware, permanent (unless you swap your motherboard). I have my old NAS registered at the hardware level so no matter how many times I’ve reinstalled Windows, it sticks.
Mass grave is bullet proof and 100% safe. The only way MS can kill it is if they completely retool their Windows registration system and the odds of that are about the same as them making Windows respect your privacy.