For those of us with a raspberry pi or intel nuc on hand, sure, it only takes 30 minutes.
This service is for people who want to kill ads at the DNS level without dealing with the hardware / setup of pihole.
Also, not many people are going to bother setting up a VPN to access their pihole DNS when traveling or on cellular, which makes NextDNS attractive.
The other argument is "just use ublock matrix". The counter-argument is it doesn't block native app ads / tracking. (One of the #1 blocked domains on my pihole is from Dashlane's MacOS app, constantly wanting to phone home)