Our 7 year old grandson loves using the phone with the MTH app. He asks now if he can use that, before having to use the remote.
Does the app alone cause the excitement? I would only guess that it adds to the enjoyment as long as it works correctly. These young children are very tech heavy. We used to go out and play baseball and games. They play it online or on their electronics. Adding the app may help tie the toy trains to modern games.