Comment by fpater

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.