I have it. Worth it? Depends on your perception of worth. For a SHTF carbine, in which it has to be as reliable as possible, the $150 is worth it. For a range rifle, probably not.
The package includes enhanced disconnector & mag catch springs, extractor spring, heavy buffer, and feedramp mod, gas port mod, and some other modifications.
For me, it was well worth it. That carbine has been flawless to date. For example, saw 2000 rounds in 3 days with Pat Rogers, no problems in a hot, sandy, dirty environment.
I recommend the SAW enhanced mags as well.