I've got a Stillen on my 2009 G37S (mechanically identical to yours). No issues whatsoever, lots of HP and torque all around. Not a single misgiving. We've been having a considerable discussion over on MyG37S where I've listed several things of importance there.
One is an oil cooler - absolutely critical. And another is - if an automatic - an automatic transmission cooler. You're covered on both sides.
If you are a G37S member (or want to be), I've been adding to my comments on this thread and I also have been adding images to my library of images there.
Who has a Stillen G37 Supercharger? Numbers, pics, vids! - MyG37
Be prepared to change your supercharger oil by the book. Also carry an extra belt with you - should it break, you'll find that the dealer certainly doesn't have one and because it's a rare part number you probably won't find it at AutoZone. Change the belt on a regular schedule. Nothing inherently wrong with it, but it is doing "double duty" over the stock setup.
And you also have to watch your air filter elements. You'll start to get strange OBD-II alerts when it gets dirty. Don't mistake it for a loose gas cap or anything else - clean the two MAFs and the elements.
And great that you have the Eibach parts... this car is so much more capable with 500 horses that it needs the suspension. But think about some SPC camber adjustment on the front and rear. Alignment is critical.