Works on ios and android.
I think their free tier is very generous at 300k lookups/month; otherwise it's something cheap like 2€/month if you want unlimited lookups (i use this to block tracking on all my devices + home network)
When I want to "try for free" I'm assigned a unique ID which is then used in all DNS resolution requests. How is that even remotely tracking-safe?
The unique id is to retain settings across different devices.
Of course you have to trust them not to sell you out.
Why would it use any extra battery? The phone has to make DNS lookups whether its with the one from nextDns or from the DHCP server.
You're right, this dns solution is very unobtrusive when it comes to energy use.