Was approached by one of their in-house recruiters on LinkedIn. The recruiters were very, very competent and made the whole process as clear and straightforward as possible. It was very enjoyable, and also quick.
First was a quick phone call with the recruiter. I was asked about salary. It was refreshing to have a frank and honest conversation without the negotiation. But be prepared for this question early on. Apparently salary is also dependant on interview performance.
Second was an online test. Four questions on Hackerrank with a 90 minute limit. The questions tested basic CS knowledge like algorithms and data structures. It was very fair. The questions weren't equally difficult, so spending 1/4 of the time on each is a mistake. Luckily, I'd practised Hackerrank before, otherwise I would have bombed due to the weird standard in/out unit test thing Hackerrank uses. One annoying thing was that one or two of the test cases timed out for me. I was using Python, so I don't know if the timeout was set for C or something. Maybe I just used a sub-optimal algorithm, but I managed to talk to somebody else who ran into the same issue.
On-sight was also great. They arranged for flights and a hotel. Plenty of drink and snacks. There were three interviews, each an hour.
The technical interview was tricky but fair with two lovely interviewers. I had to write out an algorithm/pseudo-code on paper. This is harder than it sounds, and also worth practising.
The system design/architecture was also with two interviewers, and largely good. My only criticism is given that they ask questions with potentially very broad and deep answers, adding an additional constraint after 30 minutes isn't great and messes with your time planning. Maybe it's a strategy? But they were supportive.
The "fit" or "culture" interview was however terrible. It wasn't at all as advised. We barely talked about the company or their culture. Instead, a single developer who had apparently never worked with clients or outside web development interrogated me. It seemed like he was just looking for a weakness and focussed almost half the interview on something he perceived as that. He seemed friendly superficially, but unlike the other interviewers it seemed to not want me to succeed. It was almost hostile. I think he was inexperienced in people management and more of a developer than a manager. So the lack of broad experience and hostility made it very difficult to communicate well. Very surprising given that you would send such a person, especially to the only interview with one interviewer.
Ultimately, I was informed that although the technical interviewers were in favour, the fit interviewer wasn't and so I didn't get an offer. Except for the fit interview, I'd do it again.