The best, cheapest DIY form of tuning this vehicle is HPTuners, which will set you back about $500. Be advised that this isn't an LS1 or a 3800; the tuning approach is totally different, and many professional shops have totally botched tunes on these cars because they didn't understand that fact.
Do yourself a favor and just buy a BNR tune if you want more performance.
[url=http://store.badnewsracing.net/BNR
In regards to your link, in the description, under note:
NOTE: The stock fuel injectors are considered "static" and will spray non-stop at duty cycles of 93% or more. On extremely aggressive tunes we have seen them exceed 110% duty cycle. If you plan on requesting an extremely aggressive tune, it is recommended that you upgrade to larger fuel injectors.
How does that work with direct injection?