It's cheaper for me to just bump up my Adguard DNS subscription on my home router. Though I've only done limited testing to see how efficient it handles YT ads. (so far seems to work).
Honestly, the $3 CAD I spend on Adguard DNS through my router has been incredible. I'm flabbergasted when I connect to someone else's Wi-Fi and see what the Internet looks like outside my door walls.
They must be bypassing your networks DNS. I wonder if setting a rule on your gateway that forces all DNS traffic through your own would break the client. My guess is yes.
Nextdns was $22/year and worked very well for me for 3 years. I maintain my own now, but for many people it's perfectly fine to pay for a working service, not everyone wants or needs to fine tune their DNS like some. Just because it's free doesn't mean it's better and vice versa.
I deployed it for a while on my home server, but in the end, the uptime wasn't really satisfactory and I didn't want to lose my ad blocker due to fibre damages due to poor weather or similar issues, so I decided to go for NextDNS.