What is the advice on protein bars, like "Powerbar"?

I am at work and I can not really get the liberty to screw arround with powder in a high tech room.

Do you see protein bars a good way to substitute the powder? They will take a little longer to digest, but the thing is that when you mix products together you might mix the wrong chemicals in your body.

Do you believe in mixing products? Shakes and Protein Bars of different makers?