I found a setting to have the default status of the comment to be internal. That way you have to decide and take action to send it to the client. /settings/tickets -> advanced then tick the box "Ticket Comments - default to Internal instead of External"
We use QB as well and often need to make adjustments to the final invoice. So if the invoice's don't match then that can create a problem. If there is a better way please inform us.
We need this function as it is very important to MSP organizations.