Should I Take Equity Instead of Payment for Marketing an Early-Stage AI Product?

I'm a marketer, and I’ve been approached by someone who built an AI agent (a ChatGPT/Claude wrapper). It’s only 3 months old but already has an MVP, 10 paying customers, and over 100 free users.

He wants me to handle the marketing but doesn’t have the budget to pay me, so he’s offering equity instead. The catch? He doesn’t want to discuss the percentage yet, and the company isn’t registered yet.

I’m tempted to take the risk since I believe in the product and have ideas to scale it. But the marketing will be a lot of work, and I might need to spend some of my own money.

What would you do in my position? Also, how much equity should I ask for, and does the lack of registration change anything?