More like, stay away if you are running an app that has limited concurrency per worker dyno (either because your framework is single-threaded, or because your w

More like, stay away if you are running an app that has limited concurrency per worker dyno (either because your framework is single-threaded, or because your workers are CPU-bound) and you need predictable low latency. Bear in mind that it's not like Heroku does anything particularly terrible in that use case. As far as I can see, it works about as well as any standard round-robin load balancer would. It's just that if those are your requirements, you have a problem that Heroku can't magically solve for you.