Gotcha, Adguard Pro on iOS doesn't have a DNS limit but I suspect you are right and going over the free limit on NextDNS would be pretty hard to do one one device, especially a mobile device
You can point Adguard Pro and maybe even NextDNS to Mullvad's DNS Server. So I wonder if doing that is better than using Mullvad's DNS profile alone on an iOS device? Not sure, but Adguard Pro has a safari extension and more settings. So I wonder if doing that covers more?
What made you want to make the switch? I’m currently on Mint