Sure. By far the biggest issue is once you do it you are locked into using default iOS/MacOS mail apps. I’ve yet to find an alternative email client that can distinguish between your default iCloud account and your custom address.
Receiving email isn’t the issue, it’s replying from your custom address. I suppose a client that can use email aliases would work, but honestly I stopped looking for one on iOS.
It isn’t all bad though. Using iCloud’s storage and system basically means you don’t need to pay for a mail account at your domain registrar.
It’s…okay. The hardware is decent, but the software (particularly the iOS app) has always been terrible.