I have no idea who this is for. Non-technical people don't care, and this is still too complex for them. Technical people can use Fastmail or other secure, hosted options. $500 for proprietary hardware is so steep, there are software options for the Rpi that do something similar for $40!
However, I recognize the value of having my email served and saved on premises. If I could have a fairly secure and automated backup from my local files, that’s great.
If I can also use a self hosted webmail interface then I want that too.
I agree that $500 is a lot, but it’s not an absurdly large amount.