This small subwoofer delivers not a big amount of bass, but because it is not ported the clarity of the sound is very good, even considering it small size. I compared to a 8 inch Mackie (around 300 euros), and even though the Mackie would make some stuff shake in my room, it wouldnt sound as clear. My room is around 17 square meters.
I have it paired with some Presonus 3.5in monitors (for 129 Euros) and the combination works PERFECTLY. Visually, the presonus have composite cones which also fit very well with the Fostex cone.
Compared to the previously mentioned Mackie, this subwoofer would not send any noise to the Eris speakers, while the Mackie did, EVEN when it was turned off. So thumbs up for the Fostex.
The only complain I have about the subwoofer is that it only has a unbalanced RCA input and does not offer a 6.3mm jack balanced, which is pretty much standard.
Anyway, for the price I paid, and for the amount of space it takes, I dont think you can do better.