8/10 uses of redis I have encountered in the world were people using it as a slower memcached.

1/10 are using it as a hope-for-the-best "queue" instead of rabbitmq, which is bullet-proof.

The last 1/10 actually use it as a novel "database" but every one of those instances also has mysql or postgres, rendering it completely redundant.

Redis itself was, for a while, a massive open security hole when the above people would put it on the open internet, where it would to quite useful to hackers as a free lua program runner.

Isn't it good for building and querying custom indexes? Doing that with mysql or postgres is very difficult or impossible depending on hosting solution.

Or would you still prefer to build on top of memcached?