I use this setup to get mobile adblock while on Verizon (iOS sadly has never let you override the default DNS server for cellular, just wifi). It works more or less perfectly, albeit with a noticeable hit to device battery life... so much so my wife who otherwise loves PiHole on the home network refuses to use it on her iPhone.

Using iOS's built in support for browser adblockers is largely as effective and doesn't come with the battery life hit.

You can use your custom dns over https server You can use AdGuard or select your own filterlists. Nextdns.io

I use the free tier.

Im assuming this is using a custom iOS device provisioning profile to let you set your DNS for cellular in a way the UI does not? If so, interesting solution!

Does the built in blocker block ads outside of the browser though?

No, that is one advantage of the PiHole/Tailscale setup, although PiHole wont prevent ads particularly well if at all in major apps like Twitter/FB/youtube etc.