Management:
Management is very inexperienced and architected mainly around founders and insiders. Promotion opportunities for non-insiders (e.g. early joiners, CEO and founders' friends) are few and far between. If the CEO is friends with one of your direct reports, you might not have your job for long. Management decisions don't seem to forecast more than 6 months in advance, so critical decisions can seem to be made on a whim. Management is not structured like a tech company, so reviews/team growth/career growth are nonexistent. Do not expect constructive feedback, promotions, or role or career growth.
Insider culture / cronyism:
There is a culture built around early joiners and other "insiders". It is relatively commonplace for insiders to have an inside line to senior management, and the ability to act with impunity as their proxy, while everybody else has to work with the non functional HR feedback system. In one particularly egregious instance, an insider got the head of his team fired, a fact which he proudly shared across the company. Insiders are also held to a different set of standards for things like hiring and costs.
Few opportunities for female technology leaders:
Technology, which is a large part of the company, is dominated by male managers (again, insiders and founders). There are few career advancement opportunities for female engineers. At an internal event, one member of a technology team shared how HR frequently undervalued/underpaid female engineers, to the point of trying to offer two equivalent candidates (one male, one female) vastly different compensation.
Party Culture:
While IEX has strong values, internal culture most frequently revolves around drinking beer in the office. If you don't like beer, you're unlikely to become an insider, and if you're not an insider, you're unlikely to find a long term career here.