[grugdev42]

The cofounders will not put your priorities first. Their only goal is to make money for themselves. They will axe you if they feel like it.

They are not hiring a founding engineer because they want to do something nice. They've probably realised this path is cheaper than hiring an external software development company.

Don't think for a second that you will be an equal in this relationship. You will be at their beck and call. You will be forced to write bad code to get early sales.

You'll get paid less to do more. I would stay where you are.