Lots of room for creativity, innovation, and change. But as others mentioned, this depends on the company culture.
Less red tape because of the shorter line up the organization.
Faster promotion track if the company grows and you’ve already established yourself. You can also get a huge payout if the company is acquired in the future.
The bad:
Possibly not as organized vs a company with an established support group (admin, payroll, HR, etc.).
People having to perform multiple roles due to having fewer personnel.
As a counter to the 2nd bullet in the pro section, having to deal directly with top management means you’re more exposed to politics.
Possibly lower pay. But you said they’ve been around for 2 decades so maybe they’re paying well, and I’m sure you’ve considered the pay already.