Ask HN: Should I be acqui-hired or not?

I've been working at a large non-profit helping build a project that after several years is being bought by a pretty early stage startup, privately funded. They plan on incorporating the functionality I've built into their core platform and migrate all of our clients and data into their new platform. Originally they planned on bringing most of our small (4 person) team over and now it's been reduced to just me since I have the most domain knowledge, technical capability and existing relationships. I've been offered a position with more risk and more responsibility, but after negotiating, the full compensation comes out slightly below what my current compensation is. I've been told it's their upper limit and no movement is possible.

On one hand, I want to see our project 'succeed' and bring it to help more people, for our existing clients to be not be disrupted and have that experience (and line on my resume) of having spun out. It would be exciting to learn more about the industry, have a new role and continue to grow. I'm worried that the new startup doesn't appreciate the complexity involved in the migration or functionality we've designed and will fail our clients. A small side benefit is I wouldn't have to go through the interview prep and rigmarole.

On the other hand, I took a pay cut when I joined this project because I was starry eyed and believed in the vision (and still do). One could argue I already have that line on my resume now. I'm in my mid-30s now, have a family and more responsibilities and was expecting that compensation would go up. There are other startups/companies/opportunities out there that would provide more compensation and other career growth opportunities.

Any advice?