My LFS has two hooked together on their instore coral display that is effectively a 300 gallon breeder ( only 20 inches deep) - they do work very well, and on bigger tanks you hook two together on one timer. Altho' I have mucho Tunze I don't have one of these...... I have seen a homemade one using a Tunze stream plus single controller jammed into a juwel filter box.
Definitely not worth 500 USD tho, but then again far cheaper outside of US.