startup advisor : always worth it?

A startup reached out to me recently for an advisor role. They raised a series B and are operating in a space I've founded in before. They want my expertise in AI/ML, and I'm not sure how to price my services. I understand advisors generally ask for cash and/or equity. I'll be happy to hear some of you guys' experiences being an advisor, and what package do you usually get out of it. Also, any reason why i shouldn't become a startup advisor? Not sure if this matters, but * 4 yoe in AI/ML for a big tech, working in a field that want my expertise in.  * currently CEO of bootstrapped startup on autopilot in same space, and successfully exited another one last year.   * currently CTO of a stealth startup in a very different space