They're great to manage using the IPMI solution as it will give you a console and you can monitor the sensors etc. If I had to build a new router, I would use one of these two boards.
They're not cheap as they would work out to the same cost as a general x86_64 system, but they're much faster on crypto and networking and they're small with a low TDP
In the end I got a Dell Optiplex 3040 SFF w/ Intel i5 gen 6 for 200 euro.
Tried to find a small, about 5 liter chassi, but found no good alternatives. Odroid-h2 may be an option but may have problems with openwrt and uefi boot