I run one for five 20/30 gallon tanks all plumbed together with various fish/loads and it keeps up perfectly. Never any ammonia/nitrite spikes. Very cheaply made but why over-engineer such a simple concept.
The bio-wheel is different from the pics posted on this thread, have a spongy material in the center that houses benificial bacteria....I just bought another one for my new fw sump for my 125g