Overall I had a very pleasant experience with the interview process and the following will outline my experience of the process
There were in total 2 hour-long technical interviews, 2 half-hour cultural interviews and 2 take-home tests.
The 2 cultural interviews were the first and last interviews I had (the last one being with the CEO). They were pleasant and useful in getting a feel for what the company is about and also so that the company gets an idea of who you are.
The 2 technical interviews were each after a technical test but I'll go over the interviews first.
The first one was with the Head of Engineering and gave me a good idea of the issues the company faces on a technical level. What impressed me about this interview was that he was very honest about their issues and didn't want to hide anything.
The second technical interview was a group interview with 3 of the engineers and the head of engineering again. This was also in part a cultural fit interview and once again I was impressed with how candid the engineers I spoke to were. They were able to answer my question and alleviate any concerns I had.
As for the two take-home tests, the first was a general and very broad test covering many different aspects of the role. It consisted of multiple choice, long-form answer and coding challenges. None of the questions themselves were too difficult but the test as a whole was definitely tailored for the role as was demonstrated by the breadth of knowledge required.
The second test was a much more focussed test in a part of the role that is very important. Once again, this test wasn't too tricky but for those without experience in this area it would take a long time to complete. As it stood for me the test was a pleasant length and did require that I look through some documentation but this is allowed; which is, of course, sensible as that is what one would do on the job.