Another course from the CZ.NIC Academy that I attended was Advanced Linux Networking.

In addition to the necessary theory, there were practical exercises where we had a Turris Omnia available. As it turned out, it's an ideal device for these scenarios — enough ports, if you lock yourself out you still have UART access, and the performance doesn't limit you. We weren't using OpenWRT but Debian. If you want to flash your Omnia with a Debian image (tar.gz), you can find it on Tomáš Hlaváček's website.

We tried out everything we wanted, and when we didn't know something we could ask about any part of the network stack. An ideal course if you don't want to rely solely on NetworkManager.