I don't trust hangouts ever since I discovered, by accident, that if you get somebody else's invite you can set their status and messages for the invite in calendar as you want. I reported that to google to which they said it's by design if you're sending out invites to non-google accounts or if invite is received in a non-gmail client. While I understand you can't do it any differently if you want that functionality, but this was on a business account. I'd rather see limited functionality then where you can set status for the invite only in gmail/calendar and if you're non-google account or 3rd party email client you get to only view the invite.