This is the method rather than the verdict. What to test on a demo call, which quoted numbers are actually comparable across vendors, the six questions that expose a weak build in under ten minutes, and the contract terms that decide what happens when it goes wrong.
Interrupt the agent. Change your mind after it offers you a slot. Ask something adjacent to its knowledge and see whether it guesses. Ask for a human. Four minutes of that reveals more than an hour of slides, and every vendor worth buying from will be comfortable with all four.
Notice period, data portability of your transcripts and knowledge base, who owns the phone number, and whether there is a written remedy if delivery slips. A cheap monthly attached to a twelve-month term and a non-portable number is more expensive than it looks the day you want to leave.