To be fair, a lot of people use ZK wrong, then complaint about it.

For example, if you use it like a general purpose KV store like Redis, you'll have a bad time.

Another often encountered mistake is people, thinking it doesn't need to store much data, deploy ZK to a server with slow disk/network. Big mistake, as every write to ZK need to be broadcasted and synced to disk, a bottle-neck in disk and network IOPS will kill your ensembles.