Assuming that you are a young Engineer, who is technically sound and would like to do something exciting in the career (rather than play safe).
Do some due diligence about the startup, if their idea is proven and looks like they have a bright future then it would be a good idea to work for the startup.
You will learn a lot working with a startup and that experience will grow you overall. And someday with that experience under your belt, you could start something of your own.