@smilelikemiles
Tbh, I haven't switched to the EA App yet and still use Origin. As I understand it, it does remove Origin when you install it. It can coexist with Origin on your computer, and you can have both installed but you will have to reinstall Origin again after installing the EA App. But, at some point, Origin will become unavailable, but I have no idea when that will happen though. I do know some of the other helpers have made the switch and will ask them to post so you can get a clearer idea of what to expect.
As I said before, changing from Origin to the EA App will not affect the games you have on your computer, and you won't have to reload them. You'll still be able to play them by starting them with the EA App rather than Origin.
Hope this helps.