Privacy Badger focus on blocking trackers. uBlock origin blocks all kind of things Ads,Trackers,etc and so it have a higher risk of breaking sites.
Yes, they're mostly redundant. Happy uBlock Origin users should probably keep using just uBlock. People who don't use uBlock to avoid breaking websites, or just want to block trackers, should use Privacy Badger.
Another option if you wish to protect your whole network is to set up something like pi-hole or AdGuard. I recently set up pi-hole on our network. I’m shocked by the amount of blocked traffic coming from phones and windows machines. Don’t even get me started on the traffic from our smart tv.
basically they hijack dns resolution to return does not exist errors when requests are sent to the tracking systems. highly effective, but also many sites are negatively impacted by them because no one codes for failure in the web industry.