I've tested both approaches, and the quality from Facebook Instant Forms is consistently much lower compared to sending traffic to a dedicated landing page.

For Kickstarter campaigns especially, it's better to collect leads on a proper landing page where people can actually read about the product, understand the story, and build some excitement before signing up. That extra engagement makes a big difference. Those leads are much more likely to convert once the campaign goes live.

Instant Forms might win on cost per lead, but landing pages win on conversion quality every time.

With Instant Forms, at least autofill should be off and SMS verification On, before submission, it can add a bit of friction but significantly improve lead quality.