Everybody I talked to was lovely at this pre-product org. I did, however, get the sense that they were lacking in strategic vision for how they were going to achieve their mission and seemed very uncertain they even could. People seemed lacking confidence. In my experience, this usually results in significant, often catastrophic, headwinds. They didn't seem to know a lot about what they wanted, only what they found they didn't want through poor prior hiring.
The negative experience just regarding the way they conducted their loop. First, they do those IQ/personality tests, which I usually just delete. Apparently I scored the highest ever there or something. But rather than talk to everybody over a day or 2, they stretched it out to 5 rounds spread over a month. This is AT LEAST 2 rounds too many and is almost always a sign that an org doesn't know what they're trying to accomplish. I'll never know why they didn't extend an offer, especially given the only reason a company of their size would even be in the running to be competitive to acquire someone w/ my experience and talent is because I no longer care about salary or equity anymore. What really turned me off was that after all that hassle, all they sent was some generic 2-click Dear John template from their Greenhouse app after consuming that much of my time. If they're willing to treat a C-suite candidate who could have built their program in his sleep with that level of disrespect, I shudder to think how they would treat a SME. I would never tolerate that of my reports.
The TL:DR here is if you're in a loop with this org and another offer comes in whilst you're waiting - take it rather than sit on it waiting to see what comes from them. Especially since the org is especially a skunkworks/moonshot project with no guarantee of continued funding without expedited results.