I don't know what it's based on, but it works extremely well. I use Rider & WebStorm daily and I find Rider is a lot faster than Visual Studio when it comes to the Unreal Engine codebase and WebStorm seems to be a lot more reliable than VSCode nowadays (I don't know if it's at fault, but ever since copilot was integrated I find that code completion can stop working for minutes at a time. Very annoying)