It's...okay. The hardware is decent, but the software (particularly the iOS app) has always been terrible.

Pi-hole at home and pi-hole+PiVPN while away. Works perfectly

It’s top on my list of Chromium browsers

Ironic…

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.

Prepare to be continually disappointed. I switched my domain over when it was first announced, and although it certainly works, there are definitely some needed features lacking. Other than centralizing how emails are delivered, there isn't much of a benefit to using a custom email domain. Plus, I've yet to find an iOS app (other than Mail) that works with them.

Regarding migration, have you tried simply dragging and dropping the email from the old account onto the new one? I haven't used T-bird for this, but it works in Mail.

I used both a Magic Mouse and Magic Trackpad and much prefer the trackpad. I can’t work with multitouch gestures, and I’ve never had any wrist pain after using it all day.