An equivalent solution would be to spin up a $5 droplet on DO, do basic due diligence wrt security (lock down ssh, firewall, etc.) and you end up with more memory, more connections, for less money.
I realize I'm a Luddite, in the field of DevOps.
Is it just the benefit of not needing to maintain the server?
At least that's what the cloud vendors want you to believe.
Now that said there's definitely a cultural belief in startups that you should outsource everything you can. It works for some people, but I've seen it kill others because they were sending all of their revenue to their vendors. The outsource model always suffers as you scale up.
This is exactly the benefit. You don't have to do any of this stuff. For example, my organisation has two developers neither of which are experts in network security or system administration. So if can outsource this work to a 3rd party provider then that's a huge benefit. The difference in cost between a $5/month DO droplet and a $10/month managed Redis instance is negligible for us.