My requirement was to pair a sub with the PM04 Fostex monitors. The SUBmini2 handles the job very well. The bass is tight and sounds precise, no more power is needed for desktop monitoring, and the controls are unmatched for the price range. The frequency cut-off works fine, and you also get a phase inversion switch and a volume level control. The auto-standby feature is also very useful, in that it does not affect the connected monitors i.e. no popping sound is transmitted to them, and its sensitivity is enough to keep the sub on in relatively low volume levels.
As drawbacks, I may note the lack of balanced input/output connections, and the bright blue light when the sub is on, which may annoy some if placed on eye level.
In total, I'd recommend the subwoofer to pair small studio monitors and limited studio space, thanks to its plentiful and well-implemented features and sound quality for its price range.