It MAY fix the feeding problems that gen 4s are suffering from, and in some cases apparently it helps with the ejection, although I am not 100% clear on why.
There is also a replacement extractor, although there is no official program for this yet, to fix their extraction problems.
And there is also a replacement ejector, although again there is no replacement program, to fix their ejection issues.
And I believe there is a replacement trigger bar in the works as well.
Some guns are fixed by one of these parts replacements. Some need all three. Some seem to run fine out of the box.
I will probably look at buying a Gen 4 sometime in late 2012 or early 2013, by which time I am hoping they will have a clue what the f**k they're doing. I am not sure whether the problems are all generated by poorly designed parts (like the RSA) or by poorly made parts (like the extractors).
But how they came up with the idea, "let's fix the issues with the G22, and then install that new, much heavier recoil spring in the G17, which worked perfectly before" is totally outside of my ability to understand.