Super cool to see this!! I've been prototyping with NL-to-SQL recently, one problem I've stumble into is how to prevent mistakes from impacting your database, be it a hallucination or even a malicious actor who was able to send a prompt to the LLM agent. I don't have much input about the questions you asked here, but feel free to contact me (info on my profile) if you'd like to talk about those other aspects!!
I interviewed for a role there, got quick replies to my emails too. Didn't need to use any credits to do the challenge (but they mentioned that I could ask for it if I wanted to). The challenge itself was not easy, and I assume that was exactly what they were aiming for.
Besides the interview I've already talked with them and they were really friendly and eager to help (it was not a business talk, I'm doing some academic research and wanted to discuss some things regarding networks/infra-sec). I believe you just had the wrong idea, specially when you mention "some weird sales tactic".
Edit: in my experience, the code challenge made a lot of sense.
Wow, this seems really cool! You have no idea how excited I'm to give it a try. However I was unable to find a download for ubuntu... either way, I joined your mailing list and i'm hoping to hear about a version for linux soon :)
edit: actually i just had a good idea, gonna try this next weekend when gaming!