Heroku is great... if you have a small site you want to deploy quick & easy and/or don't have the basic dev/ops skills to do it yourself. It's also great if you need to scale and have a tonne of money you don't mind spending on hardware you could get for ⅛ the price.

Heroku goes out of its way to distance you from the end-product: your site. You write some code, commit, and push, and like magic it's on your website. Neat! But... why is everything so slow? Why is my available memory so abysmal? What year is this?

For the amount we currently pay Heroku to host 2 websites and 4 celery processes, I could get 18 servers with 32GB of RAM each from Hetzner.

Heroku is nifty, but their magic is stupidly expensive and from where I'm standing, not worth it.