Their process is long - but very standard.
Recruiter call, Hiring Manager interview, meet with 3 people on the team, meet with Engineering, Panel demo with a 6-10 hour prep required where you build a demo and then mock present. Then a final interview with exec for "fit". Most of the team was super friendly and it seemed the interviews went well - I got overall positive reviews from all. They are looking to see how your experience matches with the asks of the role. Often the staff interviews are given a script to ask questions from which makes things a bit formulaic but is better than them interviewing without a plan.
Negative review comes from the Recruiter interactions. They chose to email their decline with no feedback. I've had 6 separate interviews and a demo, with a total of 20+ hours invested on my end for a senior role. Sending a cheap email without any feedback is incredibly unprofessional. Be a human, pick the phone up and provide reasons why you made your decision.
If you read through many of the glassdoor reviews it sounds like the interviews with general staff are broadly good, but interactions with the recruiting staff are poor/unprofessional.