Using Docker4Drupal in Production vs. its commercial Wodby solution I've been playing with https://github.com/wodby/docker4drupal on a DigitalOcean droplet and am utterly amazed at how it all works. 

However, it recommends that people use https://wodby.com/ for production and I'm wondering if I have to; it seems like an unnecessary step when my testing has four sites running perfectly in "production mode". 

Does anybody know in what way Docker4Drupal is designed to be run in a local environment when it seems so well on a regular server?

This isn't a question of money.. Just effort. I'm a one man show and don't need dev/staging/production for what I'm working on right now.
Disclosure: I'm a Docker4Drupal maintainer and Wodby co-founder.

We do not limit usage of our images, it's MIT licensed, so if you want - go ahead and deploy the images in production. However, you'll have to do some work before that, e.g. set up a router, certificates, cron, etc. Configuring usual stuff with containers is not always obvious especially if you're not proficient with containers. Since we already handle all of this in our platform we've added this recommendation (people asked us about production). Also, stability requirements are higher for production (including freezing the docker version).

Originally, we created docker4drupal just to provide a local environment for our customers (instead of connecting Vagrant) but later it became obvious that it is valuable for many drupalers including those who do not use Wodby. In other words, historically, it was prod > local transition, not the other way around.