Re: do Heba Diffuser actually work? worth $10 ?
To be honest, the objective in a water pipe is to cool the smoke - this is done via surface area of smoke to water. logically if you place something to aid in breaking up the bubbles there is more surface area and thus a more filtered and possibly cooler smoke. Now I have no experience with the Heba but I do know that diffused is always better than not-diffused - it simply does its job better.
personally I would suggest trying a few different methods of diffusion - a simple method would be to cut 3 slits on both sides of the downstem just before the tip (slightly higher water line if you are modding an existing downstem) with a small increment from each other to allow the smoke to exit the downstem in smaller bubbles through the 3 slits.
the easiest method is to get diffusion balls or marbles that force the smoke around all of the marbles forcing the bubbles to separate as they flow up to the water line.