Hit the nail on the head. When I usually throw my 2 cents into this discussion, the issue with them comes to the amount of water that needs to pass through them to be effective. I have to use these on the water coming into my home. When you compare them to what are marketed to us in the hobby, there is simply not enough water passing through the UV
bulb itself to be effective towards any type of management. It simply breaks down to size and water passing through them. With that said, if there was a way to have an in-line UV
bulb, effectiveness would rise greatly due to more water passing through. This would then create other problems, but since no such product exists on a hobby grade level it is a pretty mute point.