Substack or Revue - what are the main differences between each newsletter platform?

I was planning on using Revue https://www.getrevue.co to launch a free newsletter with the option for subscribers to support with $ by becoming paying members. I have a good understanding of what Revue offers but I don't know much about Substack https://substack.com. Would love to hear some opinions of why you'd use one over the other.