Can't wait to see it, Birdman. Set?! How many are you making? Will they be for sale for the general public? I think that the success of any filter system design is in how effective it is and not what it is made of. Besides, I think that fiberglass is pretty durable so I don't see why it can't be as effective as the stainless steel Bakki showers. Please keep all of us posted on the type of media you use and your pond's water condition when you use it. Congrats, Steve!
As far as media type is concerned, all as I know is it is dependent on the surface area....whichever media has the most surface area should be the most effective. I don't know how the SA of bioballs is compared to that of BH, but I suspect that it should be much less. Just my rookie thought!
