I am personally inclined more towards firebase ml kit as compared to Tesseract due to its ease of usage and wide adoption by number of other developers in community. Another good thing about firebase is its backed by Google that has a lot of resources and investment to make this tool better and this tool is widely used inside its own products to eventually it will keep improving. But using firebase MLKit with iOS is not that simple it checkout this issue in firebase/ios-quickstart project. I hope this will be resolved some day and we can use firebase MLKit for both android & iOS with React Native.