Was using ddwrt few years back, but did not use adblock in it.
Cheap routers will be the main bottleneck in running services on it though.
Though I have routers which can probably run ddwrt etc but I do not want to mess with my main routers and also do not want to install something that will be hard to access/use for anyone except me.
Now I just have a VM running pihole for adblocking in my network and my router is stock.
Just buy a raspberry pi zero and install pihole or adguard on it.