I wouldn't take siren song for a demo game. It's a silly power that is to some degree a bad advert for warhammer.
You've got a good range of units that can demonstrate the finer aspects of strategy in Warhammer (Despite the criticism that can be levelled at daemons, you can make the army very strategic).
Overall, you've probably got the right idea. But I do wonder whether you should remove a fiend or two to get a few more guys in your core units. For a demo you really want to demonstrate big units and big combats, while right now they're a bit teeny.
You've got a good range of units that can demonstrate the finer aspects of strategy in Warhammer (Despite the criticism that can be levelled at daemons, you can make the army very strategic).
Overall, you've probably got the right idea. But I do wonder whether you should remove a fiend or two to get a few more guys in your core units. For a demo you really want to demonstrate big units and big combats, while right now they're a bit teeny.