I have not really focused on HA Voice as I have Google Home and Alexa devices in every corner of our home (*) .
What would HA Voice add to my Google and Alexa devices ?
(*) For me, Alexa works best for HA notifications, Ring and Eufy integrations, and Google Home & Chromecast best for HA casting of radio streams.
At the moment, not much by the sound of it - except that it’s not Google or Amazon. 
Privacy. But don’t expect HA Voice to be a drop in replacement for Google/Alexa yet.
Good point about privacy, but it is not something I am concerned about. The risks of invasion of privacy are unavoidable, unless one lives on an isolated island without internet.
Of course, one can take protectionary measures (like avoiding Alexa etc) but the advantages (for me) outshine the risks.
Most of the conversations in my house are in various languages and, aside of the occasional swearing, are not interesting for either the CIA, FBI or KGB
It is not those you really need to worry about.
It is Amazon and Google that are profiling you and then selling that profile to other firms.
Without knowing it you might be marked as a cancer risk person and your life insurance increase and you real estate loan increase in interest rate.
I know and I was joking.
I am well aware of that and basically most companies will sell our information. That is why I get so many spam email.
I do my best to opt out of sharing whenever and wherever possible, but learned to live with it.
Email spammers are sophisticated and even spam filters do often not work. The same with spam phonecalls from spoofed numbers, which is something Congress really should do something about.
In soviet Russia, apparently, you could tell when someone was listening in to your phone conversation because there were no crackles on the line.
I am EU based, so it is a lot harder for companies to gather information and also to actually approach you for sales.
Ok, so then why use HA voice over Apple Siri then (which is supposedly privacy focused)?