I've never used that one but I have this one
http://www.bigalsonline.com/BigAlsUS...ralwfermentset
pretty much the same thing but with an electric diffuser. Mine worked fine. I didn't shake the bottle but I did kinda swirl it a little bit just to get the dry stuff from the packet wet. I ended up replacing the bottle with
DIY co2 and had a lot more plant growth. Just don't shake it to hard or let the bottle get tipped over or you'll end up with a real disaster in your tank. I would pinch the hose coming from the bottle and just give it a jiggle.
Oh and double check the hose connections to make sure that the co2 is not leaking out somewhere too.