@ohBananaJoe This isn't directly related to Hey, but it's connected. I didn't ever move fully over to Hey, because my address I got was no better than my Gmail or @ Mac one and I was a bit on and off about the service. Every so often I look around at other apps and services etc. I tried Fastmail briefly, but ultimately it always just highlights that I have no issue with Email that I need to solve and that iCloud seems perfectly good.
Hey is an interesting beast. I, also, will keep an eye on it, but I think I can see why it didn't really gel with me. It's so ridgid in it's design and I'm not willing to bend myself to fit a service. For me, at least, it made reading email harder, which should never be the case.