I could have had an x86 server running with that much RAM

You only get that much memory with ARM. With x86 I think you only get 2 vcpus and 4GB of RAM. But for containers, if they run on ARM, it’s great. And Mailu has been running very smoothly so far.

As of downsides… well, it’s Oracle. But other than that, I actually find Oracle Cloud interface and offerings much more intuitive and straightforward than other big providers such as AWS or specially Azure, at least for non power users.