The interview process was very smooth. Everyone was very friendly which is important as an interview is usually stressful experience. After each phase I received feedback quickly (usually the same or next day).
The first interview was really an informal chat with a director of engineering about the company. It was a good opportunity to ask questions about culture, projects, technology, product etc.
After that, there was a remote 1h interview which was focused on data structures (coding exercise).
The last phase was onsite - a full interview loop. I was asked to write some code (similar to the phone screen). The coding interviews were mainly algorithmic but you don't need to know any specific algorithm. It was more to check my ability of solving problems. There were also system design interview (with many follow-up questions) and some behavioural/background questions.
Overall, very positive experience. I had a chance to see the office, had lunch with the team and felt the atmosphere/culture of TE. I got even a t-shirt at the end of day!
At that time I had a few other offers (similar compensations) but decided to accept ThousandEyes because I enjoyed the culture (friendly people, fun environment), tech stack (I had a chance to ask plenty of questions about frameworks, practises, processes etc), product (networking is something which I wanted to learn more in details) and enthusiasm of people (that's important because it shows if people actually like working there).