The original demo only let players use classic Sonic in Green Hill Zone, but this one allows players to try modern Sonic as well. As this is a newer build of the game, it will be much closer to what the actual game will play like. The release date is only a few weeks from now, after all.
What exactly does "just a few days" mean? Europeans can get it on the 19th, while North Americans will have to wait until the 25th. There was no Australian date announced, but it should likely follow the European release. Even if it doesn't, you can always get yourself a PSN account for another region. Regardless, the game hits Australia on November 3rd, so no worries.