Doesn't per-call pricing reduce your usage? When I see the price of a session go to >$3, for a handful of interactions I self-limit my usage.
I'd love to have an all-you-can-eat, but $100 p/m isn't compelling enough compared to copy/paste for $20 p/m via chat.
That's not to say the value doesn't exceed $100, I just don't want to pay it.