I’m using ZA free edition and so far no problem with Avast Home edition.
Unfortunately, ZA is a bit difficult to configure with eMule, therefore I may want to change it in favour of an easier firewall.
Therefore my question: Is there any free firewall that matches particularly well with Avast?
Why? Just allow server connection IN and OUT. You'll do it and it's done: emule won't worry you more.
If you have ZA Pro I agree with you but if you have the free version the KAD network won’t work, also with Pro you can open the port UDP, not with the freeware version.