This isn't really a con but the Startup Culture isn't for everyone so be really certain this is the path for you before diving in.
There is a LOT of support but definitely no hand holding here so you have to be willing to figure things out.
You also need to be super open to change and be willing to adapt and pivot in your roles and responsibilities as the company grows - those who aren't truthfully just won't thrive here.
If these sound like positives to you, you may have just found your new family!