I don't question their commitment to #nostr, but I'm very skeptical of them wanting to #decentralize, seeing as their only has info about how to sign up on their server. In fact, they even flat out state that if you have your own domain, then "Nostrcheck does not make sense for someone like you".
For people who want to run their own nostrcheck instance anyway, you can find the code here:
https://github.com/quentintaranpino/nostrcheck-api-ts
I hope that nostrcheck will prove me wrong by making the Microsoft GitHub link prominent on their site, encouraging people to run their own server, and listing independently run nostrcheck servers instead of directing everyone to the nostrcheck.me instance. If they did that, I'd completely take back any questions about them bring committed to #decentralization.