And if security is a concern, or/and you want your dynos to talk to each other, they now have Private Spaces (https://www.heroku.com/private-spaces).
Simply said they are taking the "managed services" experience to a whole new level imo.
Plus, you may not care about that, but they actually have a UI/UX team that can design beautiful AND usable dashboards.
(Note: I don't work at Heroku, just a happy user)
But, in the end I realised I can replicate most - if not all - of it with docker cloud and github. Most CI services support github anyways, so that's also covered.
And it's significantly cheaper, for my case we have 90% price reduction - paying only for instances + docker cloud.
Not connected with any service.
I basically outsourced my cloud platform developers.
I don't see Heroku as a very long term solution for us but for the time being, while still a one-man tech team, it just means one less thing I need to deal with. Until I do ...
I can't recall a single time I had a problem deploying to Heroku, including the first deploys. Heroku is lightyears ahead of EB. Speaking of deployment, I might try Convox sometime in the future.
OTOH you can use RDS with Heroku, just be careful to have them in the same region.
In your example of security, you take an increased risk due to attacks on shared services, but I'd suggest that only a small fraction of "production" apps can field as qualified security teams as Heroku can provide... so if Heroku's customers all moved to EC2 there'd be an increase in badly managed and unpatched instances.
It makes spinning up and trying an idea very fast.
For the projects that end up having lots of users, I move to GCE or AWS
But now EC2 is offering managed databases through RDS and elastic bean stalk gives you git style deployment similar to Heroku I don't see what Heroku is offering other than another point of failure and another set of security problems. It looks like Heroku uses linux containers for isolation. So not only do you have to worry about someone attacking the underlying EC2 VMs Heroku uses but you have to worry about the tenants collocated on your Heroku VM attacking you through the linux kernel as well.