Pros
I've been at Tanium for less than a year, and I can already tell that this company is one that will take care of its employees for years. I can only speak from the engineering side of things, but I have experienced some of the most collaborative and motivating experiences in my career. Things move quickly, but everyone is available at all times (during the work day, but sometimes even after) to troubleshoot or answer questions. Unlimited PTO and being 100% remote is a plus, but I've not seen anyone abuse this system. The atmosphere is professional, collegial, and respectful. The company structure is also very flat, which means that many, if not all, of the "higher-ups" are fully engaged with what's happening on the ground.
Cons
Things are fluid and fast-paced, which requires a lot of rapid critical thinking and putting out of fires. Also, because of the highly collaborative work environment, it may be difficult for success-driven employees to find a good work-life balance.