Is it open source?

They do run a public DNS server that is equivalent to a Pihole.

It's worth trying on devices where you can't install ad blocking software, but can change the TCP/IP settings.

You can also install AdGuard home as a home-assistant add-on, and then configure your router to hand that IP out as the network DNS server -- so all of your network traffic is ad blocking as soon as it hits your wifi. (like a pihole).

It's pretty slick, highly recommend. (Also super useful to see what devices are reaching out to where and how frequently, custom block lists, custom local DNS entries, etc).

Their self-hosted product (AdGuard Home) is. ;)

yes, and it will happily run on a reasonable OpenWRT system such as a GL.iNet Flint 2.

best thing is that it works even without their app, just change dns in settings