I think what the previous poster was referring to is that the filings for the SPAC (acquisition company) are the same as any other IPO, but there's nothing in the SPAC (just money and a management team). For the company that gets acquired by the SPAC, however, it's a different story. That company does not have to go through the IPO process itself, so it goes public with a lot less regulatory scrutiny than it would have had had it pursued an IPO itself.
That's not really true though. The SPAC needs to file an S-4 before the deSPAC (the merger), which informs investors in minute detail about the target company and the merger deal. I don't know exactly how it compares to an S-1, but it's extremely comprehensive.
The biggest difference I can see is that a traditional IPO can't succeed without getting institutional investors onboard, and there are strict guidelines about what can be pitched to them. The negotiations between a SPAC and its target company are much less constrained.
I'm not an expert in this, so I'm probably wrong on some of the details, but my company is undergoing a SPAC merger, so I've tried to inform myself on how it works.
