Controversial take: as an insider, you are in a strong position to determine the value of the options. Is your company under- or overvalued? Is your product better or worse than people think? Is the company culture and morale greater or lesser than average? Are you excited to get up in the morning or do you dread each moment of work? Do you care about the content of your work, the field that your in, solving your customers problems, or are you interested only in your own engineering problems? Are business decisions made primarily by ego, the boss's gut, office politics, or do good data and clear explanations win arguments regardless of who makes them?

Startups are high risk, especially if you have all your eggs in 1 basket. Whether it's reasonable to take the risk depends on data points that only you can ascertain.

The hard part is being honest with yourself. If you've invested 4 years into this job, you surely have emotional attachments to it that transcend economics. Feelings of loyalty are good and normal. One key question to ask is how much loyalty do the founders feel to you? Would it be hard for them to replace you? Do they treat you with respect and camaraderie or like a machine that produces algorithms? Are they competent, inspiring people that you learn from, or "idea guys" who are good at pitching but not much else? If you were the CEO, would you hire them?

Just a few of the questions I would ask myself in your shoes.