I have a goniometer I bought last time, but don't plan to use it this time, or at least not until my ROM feels and looks about right. I don't know what a "good" or "bad" ROM is at any given point, I just know what matters is your ability to function well when all the swelling goes down at a much later date than three weeks. I don't know how accurate the apps are, probably not that accurate, but I don't have any actual knowledge about them, just guessing. Don't get stuck on numbers, especially this early. Right now it's more important that you rest, ice and elevate a lot, along with those ADLs and activity progressions.