I have modest needs from Redis -- basically I want a queue ~1000 items long, under 1MB per item.

I could provision a couple of EC2 servers, get Redis going on them, set up some sort of monitoring, some failover mechanism, etc. $X/month.

Or I could pay someone $Y/month to give me a Redis server I can use, and not have to care about the rest, so I can spend time worrying about things more relevant to my actual goals.

If $Y is not much more than $X, it's a very easy decision.