Can't say enough positive things about my experience interviewing at Mixpanel.
I was reached out to about a position as a Senior Developer. It didn't quite line up with my recent experience in a management role, but I thought, hey why not. I've used the product quite a bit and I think the specific tasks for this role seem interesting.
They really put me through the ringer. A hiring manager screen, technical rounds, more soft skill rounds, and even a portfolio review! This last interview is extremely uncommon for any engineering position, but they needed to know that I had many intersecting design and leadership skills--including the ability to present and persuade. It was a perfect fit for me personally, really quite tailored to my background. Which is rare. It sounded like they required the same for other candidates, which I can imagine being a little frustrated about if they didn't have my exact experience and strengths.
Anyway, what really helped me shine was the incredibly helpful talent partner, who did absolutely everything in their power to set me up for success. They were honest, transparent, and made themselves fully available to me for any questions I had. They also updated me like clockwork on feedback and status.
When I had concerns, they got the VP to talk through it with me directly, who I'm sure is a very busy person. This was also very much appreciated.
When interviewing with several opportunities, you really get a full spectrum of professionalism and competence. I can speak with authority when I say that interviewing at Mixpanel has been a highlight for me, despite being quite an intense process.