Is this that bad? At our company we are using redis for real time recommendations. And this is our primary database for storing accumulated statistics about items and users. It has been important to us to have a quick way to share the data between the workers and we chose redis.
You're fine. The simplistic interface that Redis provides to sets, and therefore empowering pragmatic recommendation engines, is the perfect tool for this job.
There's nothing a priori wrong with using redis as a primary data store if your data is temporal and your durability needs are aligned with it's model.
