Isn't talking to a dead person's Echo unhealthy?

It can be, if it is built badly, and that is why it is built with rules: your Echo says what it is in its first reply, never asks to be visited, never promises a future, never says what you "would have wanted" beyond what you actually said, and steps out of the role entirely if someone seems in crisis. It never contacts anyone first. Those rules follow published work on grief and on responsible use of this kind of system — see Method.