http://www.stmpo.com/product.php?productid=16135&cat=250&page=1
I feel its really necessary to bolt on if you have a targa NSX. And if you have a coupe, it just makes the chassis more stiff which is always a good thing. Well worth the money.
It appears to serve the same function as the NSX-R bars I installed when I first got my car. I like the NSX-R bars as they are a JDM part designed by Honda for the car and they are made of Aluminum, no chance of corosive action between steel and aluminum. I would make sure that there is something isolating the steel from the aluminum besides paint, the only problem is then you might lose some rigidity.
They did make a difference especially with the T-top not torquing as much during high load cornering. But the NSX-R bars are 2 bars, one high and one low and I would think they would provide more rigidity than this single bar, think of it as holding something high and low with 4 hands instead of 2.
Good luck on your project sounds great, hope you get it finished in time to bring it to the Autocross on September 19th.
Tytus