Initial HR call is very informative and well structured, they tell a lot about the company, current projects and team. HR is friendly, responds fast and helps if you need to reschedule meetings. Next interview is so called "Value based exchange" with COO. This part is a bit weird, first you have to watch a video where COO explains company values and principles and then on the meeting you discuss them. There are no certain criteria on how they assess you. My guess COO just needs to like you and you should tell about your experience in a very enthusiastic way and sell yourself. This is a small company and I guess they value personal qualities more than skills (that is why this interview goes before any tech assessment).