I have one, it did the square root of f-all.
Just so you know, i think it is a very mixed batch of results, I suppose it depends on how well the stock grounding is. I wouldn't go spending £200 on one, just get a £40 job off ebay and if it doesn't work then no big loss.
Also if you have a lumpy idle then try removing your throttle body and giving it a good clean with a mechanical cleaning spray and do and ECU reset. I found that to be the biggest help. The TB gets filthy after a while. (oh be careful not to nudje/adjust the butterfly valve inside the TB by mistake).
R