We use Gatsby for our landing[0] (and are also in the process of moving the main SaaS dashboard to it) and the experience has been nothing but amazing. Page loads almost instantly with little manual optimization required and compile time rendering makes deployment really simple - unlike Next.js you do not have to fiddle with production SSR using serverless functions or a separate node server. The only issue with Gatsby is that compile-time SSR errors are not exposed during normal development live reload so everything needs to be compiled twice, once for development and once to test that the production build can be generated without error.

[0] https://narrationbox.com