Many browsers/apps now will ignore the system/DHCP-provided DNS server and use their own though (often via TLS so you can't block it easily)... so while this might work for some situations, I can't in good conscious call it a great solution.

Wow I did not know that.

I agree. It's not a very robust solution, but it's better than nothing at all .

And it's annoying sometimes. One thing I found is that it somehow forces Google safe-search, which appears to block some non-pornographic search results.

I understand that. I just wasn't sure if Reddit and co used specific subdomains for porn images/videos.