Looking to implement the best way to save levels across devices for my simple unity game app. We only save levels locally currently and its standard save where player got up to, other levels are locked until they are unlocked by winning last level.

This is for both iOS and Android. I've seen 3 methods, I currently have firebase integrated and saw they offer this option also.

https://firebase.google.com/docs/database/unity/save-data​​ [FIREBASE]

https://developers.google.com/games/services/common/concepts/savedgames​​ [ANDROID]

https://developer.apple.com/library/archive/documentation/NetworkingInternet/Conceptual/GameKit_Guide/SavedGames/SavedGames.html​​ [IOS]

I'm trying to weigh the pros/cons to which method I use. With firebase it means it only needs to be configured once for both device types whereas if I do it natively it would be a bit more work? But then what about costs, would it be more better to rely on google/apple cloud to store compared to firebase? Its a relatively small simple game so I can imagine save file would be much at all.

Any advice would be much appreciated.