I have 2 of them, and the bigger pond version. I think they are fantastic internal filters. I use both for mechanical filtration and surface agitation/oxygenation in my Panaque tanks, and they've yet to clog even with completely soiled media. They are very powerful at 1200lph, coming out of a small aperture, but with high power consumption at 28 watts. With a tank smaller than 120cm/4' they are probably too powerful. They fit in the tank with either suckers or hangers. They are large and depending on your tank could be difficult to accommodate.
They are hard to find, and expensive. I've been lucky with 2 of mine found on Ebay.
An very good and powerful filter but too much for smaller tanks.
This is the pond version
