Does Migratify import customers, orders, or reviews?

No. Migratify imports products only: their content, images, variants, and pricing. See What product data does Migratify import?

Customers, orders, reviews, gift cards, and store settings are outside what Migratify migrates. For those, use Shopify's own import tools or a dedicated migration service.

Collections aren't imported either, but you can send every product from an import into one of your existing manual collections with the Add to collection import setting.