Render has been my drop-in successor to Heroku. No complaints except their weird team pricing, which doesn't matter for solo projects

Render didn't support Docker images last I checked, and the worst part of Heroku and cloning it was not actually having a locally reproducible build image. I want to deploy what I've built locally, not hand my source over to some magical pipeline.

Different strokes. Personally I avoid Docker in favor of source-code-deployment; the "magical pipeline" is usually just "git pull and then run a provided command". But Render does support Dockerfiles for eg. installing a runtime like Deno that isn't provided out of the box

We recently added support for deploying images from container registries. Currently in early access.

If you're deploying an Elixir/Phoenix app, then Gigalixir has worked really well for me. It's expensive, but then so is Heroku.

What’s their reliability been like?

Am I right in thinking the platform got bought a little while ago, and it’s being run by a relatively small outfit?

I've been using them for the last ~10 months or so to run http://PhoenixOnRails.com. Gigalixir have been 100% reliable for me so far, but it's a low-traffic app - I can't tell you what it's like to run a big app on them at scale.

I don't know who owns them but I do get the impression it's a small team. Hasn't been an issue for me so far. Their customer service has been very helpful and responsive on the rare occasions I've needed to contact them

Scalingo is a good drop-in replacement for Heroku. They even use Heorku build packs. They've got good support and are an EU company with hosting in EU (if that's important to you).