Pros
An opportunity to change the world, though the company has diverged from the grassroots impact it originally aimed for. Nice people overall. Quitting feels as relieving as breaking up with an unreasonable demanding girlfriend.
Cons
The founders bag clients through over-promising. They suffer from acute optimism about their capabilities. But when things fall inevitably behind schedule, you're expected to work weekends without compensatory offs, work late without overtime, make false claims to clients to save face, until your mental health and family life begin to suffer and you decide to quit. One of the founders has a bad attitude and is a micromanaging task master. You'll be blamed for not meeting unrealistic expectations, given hell for taking a day off sick or relaxing one weekend, and generally be treated like an employee and not a colleague. You won't be working directly under this person if you're in tech.