I'm not too happy about the deathknight either. I'm not happy about the idea of having to control 2 characters at the same time, that sounds quite stressful. I hope their next Divinity game after BD won't be a RTS (that was a JOKE, so shut up).
I have faith in the Larians (I think they will probably make it work), but I'll definitely not buy it without playing the demo first.
To control 2 characters at the same time is not easy.
But an easy game is not fun.
At the beginning it would be stressful, but as you play you would get used to it.
For instance, with Imprunner when i began to play i was killed in the level 1, then i get used to the game and i made good progress.
I completely agree with you, i never buy a game without playing a demo first.