Seriously, using something devoid of thought as "a sparring partner for your thoughts" seems to me like it's a serious entry point to losing one's grip.
Especially since the behaviour of those machines is steered by large corporations whose only goal is to get your ressources, be it money, skill or attention.
The thing with signal on iOS is simply that there currently is no way to back up your messages.
And I'm kind of going to be a bit pissed if the only way to back up my messages will be to use signal's servers after this feature is released.