Lots of older threads about this. If some ADR isn't available when you first make your plans, you might have better luck closer to when you travel since people will cancel their plans to avoid that no-show fee. I wouldn't bother constantly checking prior to your trip. Look up what is now available a couple of days ahead of time when at Disney will work better and you don't have to be constantly checking your phone.
Not sure some 3rd party will be any better since if there are thousands of others also looking for ADR's, by the time you get their notification, someone else has probably already booked it.