JSX file is slow unless translated (compiled) on the server. That is, one has to download numerous NodeJS packages which you will probably never check.
Downloading numerous packages whose code is largely unchecked is a real security threat which has already been successfully exploited by hackers.
Large companies can replace potentially dangerous repositories like npmjs.com with their local mirrors, where they store only selected packages.
If your company is not huge or has not too much money to waste, replace ReactJS with either KnockoutJS or DB.js
Press F12 to see how much data one has to download, even for a simple web page. For someone with fiber-cable internet, the difference might be insignificant, but not everyone and not always has high speed internet.
ReactJS requires a lot of RAM. One can feel this for computers with less than 10 Gb of RAM.
ReactJS code is too long, see an example below (simple calculator using ReactJS and DB.js).
With ReactJS, I have to separate HTML from the code; with DB.js, one can embed all JavaScript code into HTML.
One can master KnockoutJS or DB.js in a week; ReactJS is harder to learn.