Are Portals of Power cross-platform compatible

I figured it out myself:

You have to sign in with a user, otherwise the game will not save (but will not warn you that it is not saving).

They function more or less the same as in the first Skylanders game. The level you unlock is the same, and has the same storyline, but the gameplay might be a little different since they took the same level layout but used enemies from Sky: Giants instead of just using the enemies from Sky1. You can use it as a powerup item mid-level, although it might ask you if you want to play the Adventure level.