The quality on that spoiler isn't great - I have one but haven't put it on yet. The spoiler itself is a bit cheap and the mounting for the tube isn't what I would call professional - just zip ties. Also I suspect the quality of the duct tube too - it looks very cheap.
Combined with the Quantum parts it would probably work okay - just not on it's own. I was thinking of getting a standard air-dam and cutting the holes in myself using the quantum ducts -
http://store.quantummotorsports.com/...products_id=67