It seems you can download the ISO directly from Microsoft, or from that site, and use their script to activate it.
I haven't had the opportunity to test it yet, but seems "legit" to me.
The guide is on the site they linked. It works, I did it a few times. They have to mirror the LTSC installation files unfortunately, but there's a guide on how to verify they're genuine if you don't trust them.
i'm the pirate of the biggest seas but even i wouldn't pirate my os. if im gonna dual-boot, i will buy win10 2019 ltsc. it is survivable, key resellérs have ok deals
Honestly, the way Massgrave works seems less sketchy than random keys from resellers. Massgrave is able to trick Microsoft into giving you a legit license key.