This doesn't really replace something like haproxy. In the diagrams, the "real" servers that they are load balancing to are L7 load balancers like HAProxy (using https://github.com/facebook/proxygen most likely)

The problem this solves is is when you are using haproxy but need redundancy or a single server is no longer capable of handling the load and you need to scale out to 2+ servers.

You could run 4 haproxy servers and use round robin DNS to load balance between them, but as they say, this has the problem of:

> compared to DNS it doesn't need to wait for TTL to redirect traffic from failed L7 lb.

Many people likely use anycast/ECMP for this case, but that has the other issue they mention:

> compared to anycast-based solution, L4 lbs are more resilient to the networking related issues (which triggers mass ECMP reshuffle)/ enable better handling of adding/removing of L7 lbs from the pool as well as provide better support for unequal load balancing.