"Very very slow" might be a bit of an overstatement. The initial React render for that page takes 200ms on a MacBook. A release build will speed that up slightly, and cut down the bundle a little, but in the scheme of things it's not going to be noticeable to the end user.

If you actually wanted the page to feel fast you would probably do something like <script>document.write(window.navigator.userAgent)</script>