The interview process is a bit long and unnecessary. You start with a pre-screen call and if you pass that, you move on to three coding challenges. Each of these are separated by a week, so you are investing at least four weeks into their process.
The first few interviews I had were actually very pleasant. The interviewers were very engaging, and the coding challenges were a collaborative effort. I dare say that I actually had fun during this part of the interview process. Feedback was almost immediate, and I kept moving on. Until the last interviewer.
When we started our call, there was no pleasantries. He lead with "I was instructed to give you a coding challenge, so I guess that's what we are doing." He also stated that he wanted 10 minutes afterward to talk, so I cut things short so we could chat after.
During the challenge, however, it was not like the other two at all. He clearly did not want to be there, and responded to any attempts at conversation or questions with terse remarks or something like "google it". When we got to the last 10 minutes, we ended up talking for about 2 before he concluded the interview. Even then, it was me mostly asking questions and he wasn't asking me anything.
After this, it took over a week to get a response from them (when before I had a response within 24 hours). Finally, It was a simple "we decided not to continue." -- but why? I aced two of the challenges and got through 95% of the third. I guess that 5% mattered a lot more than I thought.
Bottom line, while their product is very interesting and it seems like a great place to work, don't waste your time with their interview process. At the very least, if you do, keep talking to other companies while you wait.