Never heard of it, but giving the demo's a once-over if this is typical of the code they vomit up:
gatsbyjs.github.io/gatsby-starter-default
I would NOT suggest using it. They seem to have a raging chodo for inlining style in the markup which means a missed caching opportunity. In general their entire site and much of the methodologies listed in their tutorials
So like most of this nonsense, my advice is just say "no" -- unless you WANT to tell users with accessibility needs to go plow themselves and deploy ten times the code needed to do the job.
The real laugh being their output is minified and it's STILL 11k of markup to deliver 100 bytes of plaintext -- not even 1k's flipping JOB. Admittedly 9.9k of that is all the style that has ZERO BLASTED BUSINESS IN THE MARKUP, but even that's a bloated mess; a laundry list of how NOT to build a website. Don't even get me STARTED about the train wreck of hardcoded CSR in that bloated script.
To be brutally frank if all of those "data-react" attributes slopped onto things JavaScript has zero blasted business even touching, inlined style="", static STYLE tags, pixel max-width with EM content, lack of condensed properties in the stylesheets, and host of other "I cans haz teh intarwebs" ineptitude doesn't tell you these people have NO business telling others how to make websites, nothing well.
Just once I'd like to see one of these things where the code didn't just scream "For people who know nothing about building websites, BY people who know NOTHING about building websites."
This one only reinforces my belief that such systems are incapable of producing quality websites. They are universally bloated trash flipping the bird at accessibility, chewing on bandwidth for nothing, and overflowing with bad practices. I hate to use the words as I do resort to them far, far too often, but these types of "shortcuts" simply reek of ignorance, ineptitude, and incompetence.
Apologies to all if that's too "harsh", or "offensive", or gets your knickers in a twist, but that's the TRUTH of it! Truth hurts, that's why it's so unpopular.
Alternatives? You want to write a static site, just write a static site! Or go simpler by just leveraging whatever your server side language is to divide up the common parts from your content -- the old "poor man's" approach.