They work good on a pressure pump, but defeat the benefits of a high flow/low pressure pump(aka Dart). If you don't want to run big piping all around for your dart style pump then a pressure biased pump and some eductors get you good flow with smaller piping. KTH was pretty good about matching up a pump based on it's curve to how many eductors of certain sizes you would need. I've got a 3/8" or 1/2" orifice one on my 40 breeder frag tank and the change in flow is pretty dramatic with the eductor installed. I run a mid-range reeflo uno series pump to feed the breeder, ozone reactor, and supply to my 180 display upstairs.