I really like them but they do have two downsides for "more advanced" users (or at least for me) - it is a home device as after all.
- No support for VLAN or VLAN tagging - you can set up you WiFi and a guest WiFi. You can also map the guest network to an Ethernet port. But that's about it.
- There is no way to change the DNS suffix (*. fritz.box) to another value - I do own a domain that I use for the local services on my home server, etc. which then allows for Let's Encrypt certificates, but I cannot use it "out of the box".
If you're an advanced user, there's plenty of ways around that, though. I just wished that these two thing were to exist in the firmware to have less work with my home infrastructure.