Just checked them out correct me if I'm wrong but they seem more like an alternative to rackspace or EC2. They provide a VM while heroku provides the full preconfigured application and deployment stack.
I've been experimenting with Cloud66. Currently everything I have is on heroku. I'm going to be moving a few things over to cloud66.
It's definitely a little bit more work, but once you get over the learning curve and have your manifest/post-deploy hooks setup correctly... It's pretty much auto pilot. Scaling and deployment are a breeze.
I'm running it with digitalocean. Going to be saving a lot of $$.
My favorite part is running my own redis and memcached. No more need for expensive add-ons.