If you like autonomy this is a great place to work. I've had exciting opportunities to make suggestions towards operational strategies, all of which have been taken seriously and some implemented.
The management team has been supportive of my professional development!
Cons
As with any start-up, there are good times and not so good times. It can be hard when there's uncertainty.
If you believe in the mission, this is a great place to be. The CEO is all about helping employees follow their "life-plan" and will do whatever it takes to keep you on track.
The CEO often talks in metaphors and it can be difficult for a linear person to follow what he's saying. That said, what he says is deeply inspirational if you grasp his meaning. It's important to have team members who can interpret him for the rest of the group. The mission is very clear.
Cons
There are a few bad eggs on the team who let negativity impact the energy of the group and the C level team is too busy to weed them out. It's unfortunate to have a team of driven people, who are guided by saving lives, ruined by individuals who are only here for the paycheque.