[electron react] Any documents about these two clients?

Or any user report on the user experiences?
How similar or different are the two clients?

Got it from the build doc: BUILD.md

React client is probably used for mobile application:

Building the Mobile application

First you need to setup React Native to build projects with native code. For this, follow the instructions on the Get Startedtutorial, in the “Building Projects with Native Code” tab.

Electron is for Desktop builds:

Building the Electron application

cd ElectronClient/app
rsync --delete -a ../../ReactNativeClient/lib/ lib/
npm install
yarn dist