I second this. With IPv6 turned on and custom DNS servers, the eero still tells all the clients to use my ISP's IPv6 servers (along with the custom IPv4 servers), so it kind of defeats the purpose of setting custom DNS.... :-(
^What Sal said. I use a raspberry pi running pi-hole as my local DNS server and would like to be able to turn on IPv6, but then my network uses my ISPs DNS instead of my RasPi. A fix for this would be greatly appreciated.
Of course, proper network traffic monitoring and logging would help as well.