It was a very thorough interview process and a lot longer than many other places. I think you need to be pretty sure that you want to work at Bumble before you start this process otherwise it might feel like it's dragging on too long. I was attracted to the company so I felt the interview process was a good opportunity to make sure that I would be a good fit. I wouldn't want to do this process if I were interviewing at five or six places, but because I was only in their process it wasn't bad to spend effort on making sure it was a good fit.
There was a lot of opportunity to ask questions about the tech stack. I really hate it when companies hide the skeletons during the interview process and I arrive to discover that I'm working for a bunch of serial killers who sweep their body count under the carpet until they swan off to another company.
The interviewers were extremely knowledgeable and asked some pretty tough questions. Bumble has 500 million users so there are some very real engineering challenges around scaling, concurrency, and performance. I haven't had a lot of (any) experience working on that scale so quite a few of the questions were theoretical to me rather than based on my practical experience.
One thing that has really stood out for me is that my working experience at Bumble has been exactly what I expected from the interview process.
I think overall that last point is the most important reason for giving this a positive interview process.